<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2024 Workiva-->
<!--r:04a5eb84-969f-40d4-a3a1-1b8194336285,g:23e06efd-aae2-4ac4-9e2f-2e21516b066d-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://gig.com/role/CoverPage" xlink:type="simple" xlink:href="gct-20231231.xsd#CoverPage"/>
  <link:definitionLink xlink:role="http://gig.com/role/CoverPage" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_89831d1b-37e5-4ad5-86d1-b4a5475d3789" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_DocumentInformationTable_89831d1b-37e5-4ad5-86d1-b4a5475d3789" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_45c9e6c0-8df3-4e16-8146-6e999ba5c77d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_89831d1b-37e5-4ad5-86d1-b4a5475d3789" xlink:to="loc_us-gaap_StatementClassOfStockAxis_45c9e6c0-8df3-4e16-8146-6e999ba5c77d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_45c9e6c0-8df3-4e16-8146-6e999ba5c77d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_45c9e6c0-8df3-4e16-8146-6e999ba5c77d" xlink:to="loc_us-gaap_ClassOfStockDomain_45c9e6c0-8df3-4e16-8146-6e999ba5c77d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_5550ede3-6412-484b-99ca-5e78f65a30db" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_45c9e6c0-8df3-4e16-8146-6e999ba5c77d" xlink:to="loc_us-gaap_ClassOfStockDomain_5550ede3-6412-484b-99ca-5e78f65a30db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_6f1ad71d-c299-4044-8be8-85b6837df66f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_5550ede3-6412-484b-99ca-5e78f65a30db" xlink:to="loc_us-gaap_CommonStockMember_6f1ad71d-c299-4044-8be8-85b6837df66f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_ea556a75-3ee8-4988-834b-8e5fae12654c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CommonStockMember_6f1ad71d-c299-4044-8be8-85b6837df66f" xlink:to="loc_us-gaap_CommonClassAMember_ea556a75-3ee8-4988-834b-8e5fae12654c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_13b001c6-8d82-47bb-9ce9-70e077552fa7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CommonStockMember_6f1ad71d-c299-4044-8be8-85b6837df66f" xlink:to="loc_us-gaap_CommonClassBMember_13b001c6-8d82-47bb-9ce9-70e077552fa7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_2223f614-e53c-433d-8b32-5fea0969bf08" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_DocumentType_2223f614-e53c-433d-8b32-5fea0969bf08" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentAnnualReport_40b0b708-93fe-4b4b-ad98-66bb5cc135a5" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentAnnualReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_DocumentAnnualReport_40b0b708-93fe-4b4b-ad98-66bb5cc135a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_411ac1a0-4640-411e-9cfb-abeaf3dd94a1" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_CurrentFiscalYearEndDate_411ac1a0-4640-411e-9cfb-abeaf3dd94a1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_9d106020-6206-4b00-bea1-5abedad4b1c7" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_DocumentPeriodEndDate_9d106020-6206-4b00-bea1-5abedad4b1c7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_9345cbfa-5a7f-43dc-9b48-8c8819b43f51" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_DocumentTransitionReport_9345cbfa-5a7f-43dc-9b48-8c8819b43f51" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_fa184be3-aeb6-4d07-bd6c-2ad9065162f1" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_EntityFileNumber_fa184be3-aeb6-4d07-bd6c-2ad9065162f1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_9c2bf254-04c3-467d-b382-2dc7a556fa59" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_EntityRegistrantName_9c2bf254-04c3-467d-b382-2dc7a556fa59" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_e7b991f0-5886-4f5d-a8e3-82c5f47d5764" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_EntityIncorporationStateCountryCode_e7b991f0-5886-4f5d-a8e3-82c5f47d5764" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_7d9d396a-71df-4ef2-b673-84597b293e28" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_EntityTaxIdentificationNumber_7d9d396a-71df-4ef2-b673-84597b293e28" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_49e1949a-e33c-4df7-9044-1daa66a28e43" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_EntityAddressAddressLine1_49e1949a-e33c-4df7-9044-1daa66a28e43" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_83091c3a-879f-4d2d-b625-374d65b74469" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_EntityAddressCityOrTown_83091c3a-879f-4d2d-b625-374d65b74469" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_590c99c3-8118-465b-b7e4-ef6b7e69d777" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_EntityAddressStateOrProvince_590c99c3-8118-465b-b7e4-ef6b7e69d777" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_e7c6d557-9063-4d29-8c31-9c9cfcfe5dd9" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_EntityAddressPostalZipCode_e7c6d557-9063-4d29-8c31-9c9cfcfe5dd9" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCountry_ee413361-e391-4508-a392-9531d6cd257d" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityAddressCountry"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_EntityAddressCountry_ee413361-e391-4508-a392-9531d6cd257d" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_da56e2ad-bc68-427b-8632-59f04e111a18" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_CityAreaCode_da56e2ad-bc68-427b-8632-59f04e111a18" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_b6a47d5e-bd04-4365-b162-49980083d6e0" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_LocalPhoneNumber_b6a47d5e-bd04-4365-b162-49980083d6e0" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_775f9645-5412-44e6-a150-ab71fd0b3d14" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_Security12bTitle_775f9645-5412-44e6-a150-ab71fd0b3d14" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_d315e70f-1f82-445b-ac6f-3e7be27f4be1" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_TradingSymbol_d315e70f-1f82-445b-ac6f-3e7be27f4be1" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_a973b137-1b90-4449-bd8e-45e8a4fbec32" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_SecurityExchangeName_a973b137-1b90-4449-bd8e-45e8a4fbec32" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityWellKnownSeasonedIssuer_a3c235ea-5ab7-4fee-ad89-a410684f96ab" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityWellKnownSeasonedIssuer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_EntityWellKnownSeasonedIssuer_a3c235ea-5ab7-4fee-ad89-a410684f96ab" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityVoluntaryFilers_0773e4b5-f678-4b52-a28a-c44b937cd323" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityVoluntaryFilers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_EntityVoluntaryFilers_0773e4b5-f678-4b52-a28a-c44b937cd323" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_42d93d69-2601-4343-a3d5-2002704af6bf" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_EntityCurrentReportingStatus_42d93d69-2601-4343-a3d5-2002704af6bf" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_95435512-88aa-48f3-b924-a78452505098" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_EntityInteractiveDataCurrent_95435512-88aa-48f3-b924-a78452505098" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_d80ba297-469d-4e76-b8d0-8e9c2cec0611" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_EntityFilerCategory_d80ba297-469d-4e76-b8d0-8e9c2cec0611" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_2c9c5629-3477-42c5-8566-b1ba10790c09" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_EntitySmallBusiness_2c9c5629-3477-42c5-8566-b1ba10790c09" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_fc0d22b9-8ca5-4056-b0dc-ef88926a62cd" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_EntityEmergingGrowthCompany_fc0d22b9-8ca5-4056-b0dc-ef88926a62cd" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityExTransitionPeriod_4d4dc163-2437-4c66-9de2-27c8f900748a" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityExTransitionPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_EntityExTransitionPeriod_4d4dc163-2437-4c66-9de2-27c8f900748a" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_IcfrAuditorAttestationFlag_adc68e49-71dc-4fcf-8e52-5dba102620f1" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_IcfrAuditorAttestationFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_IcfrAuditorAttestationFlag_adc68e49-71dc-4fcf-8e52-5dba102620f1" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFinStmtErrorCorrectionFlag_f847db0b-84c7-4237-b049-353ed6c8e59f" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentFinStmtErrorCorrectionFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_DocumentFinStmtErrorCorrectionFlag_f847db0b-84c7-4237-b049-353ed6c8e59f" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_2c481049-2ab5-448b-a4be-2ce02ca0acf1" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_EntityShellCompany_2c481049-2ab5-448b-a4be-2ce02ca0acf1" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityPublicFloat_aac118a7-afa7-421b-88ad-00c3f8604c11" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityPublicFloat"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_EntityPublicFloat_aac118a7-afa7-421b-88ad-00c3f8604c11" xlink:type="arc" order="30"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_e8f8c5f6-d6ac-404c-8840-fc420fe00d16" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_e8f8c5f6-d6ac-404c-8840-fc420fe00d16" xlink:type="arc" order="31"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_b93da0a2-032d-4cf8-a920-6d4a9aaea5cb" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_EntityCentralIndexKey_b93da0a2-032d-4cf8-a920-6d4a9aaea5cb" xlink:type="arc" order="32"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_3c6152dd-ec69-4930-a138-9043e663d742" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_DocumentFiscalYearFocus_3c6152dd-ec69-4930-a138-9043e663d742" xlink:type="arc" order="33"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_f4c291dc-4e42-41d4-a786-00393a8351d3" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_DocumentFiscalPeriodFocus_f4c291dc-4e42-41d4-a786-00393a8351d3" xlink:type="arc" order="34"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_3bde4d73-2f61-49fa-9499-a1f03905af55" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_3698afb6-1bd6-4834-bb0a-5fae9452739f" xlink:to="loc_dei_AmendmentFlag_3bde4d73-2f61-49fa-9499-a1f03905af55" xlink:type="arc" order="35"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/ConsolidatedBalanceSheets" xlink:type="simple" xlink:href="gct-20231231.xsd#ConsolidatedBalanceSheets"/>
  <link:definitionLink xlink:role="http://gig.com/role/ConsolidatedBalanceSheets" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_1fe9ba7f-47c1-416e-a64a-0e88adff9705" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_08473e1c-3b46-4e60-a59c-86d3d6e1ead7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_1fe9ba7f-47c1-416e-a64a-0e88adff9705" xlink:to="loc_us-gaap_StatementTable_08473e1c-3b46-4e60-a59c-86d3d6e1ead7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_de2d4d07-9b09-463a-8109-7a876d002618" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_08473e1c-3b46-4e60-a59c-86d3d6e1ead7" xlink:to="loc_us-gaap_StatementClassOfStockAxis_de2d4d07-9b09-463a-8109-7a876d002618" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_de2d4d07-9b09-463a-8109-7a876d002618_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_de2d4d07-9b09-463a-8109-7a876d002618" xlink:to="loc_us-gaap_ClassOfStockDomain_de2d4d07-9b09-463a-8109-7a876d002618_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_3cd15b3c-d791-4637-9950-dc88236b9e6f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_de2d4d07-9b09-463a-8109-7a876d002618" xlink:to="loc_us-gaap_ClassOfStockDomain_3cd15b3c-d791-4637-9950-dc88236b9e6f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_443db953-b32b-4708-a730-0f723d9cf853" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_3cd15b3c-d791-4637-9950-dc88236b9e6f" xlink:to="loc_us-gaap_CommonClassAMember_443db953-b32b-4708-a730-0f723d9cf853" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_dd6e9d1a-c700-428a-b22c-3a33487ee0d6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_3cd15b3c-d791-4637-9950-dc88236b9e6f" xlink:to="loc_us-gaap_CommonClassBMember_dd6e9d1a-c700-428a-b22c-3a33487ee0d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_4cb20fc0-6cde-4a72-980b-4b30bc9be4ce" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1fe9ba7f-47c1-416e-a64a-0e88adff9705" xlink:to="loc_us-gaap_AssetsAbstract_4cb20fc0-6cde-4a72-980b-4b30bc9be4ce" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_83a969c8-1677-4a88-b1e1-5e6ecead1b18" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_4cb20fc0-6cde-4a72-980b-4b30bc9be4ce" xlink:to="loc_us-gaap_AssetsCurrentAbstract_83a969c8-1677-4a88-b1e1-5e6ecead1b18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_85e69481-41d8-416a-8ceb-e920fccb616a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_83a969c8-1677-4a88-b1e1-5e6ecead1b18" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_85e69481-41d8-416a-8ceb-e920fccb616a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue_8b44ffd7-f79d-4424-b364-b1df339dc52d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_83a969c8-1677-4a88-b1e1-5e6ecead1b18" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue_8b44ffd7-f79d-4424-b364-b1df339dc52d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_de593360-1ea3-4a58-8d6d-fa3535ca0379" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_83a969c8-1677-4a88-b1e1-5e6ecead1b18" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_de593360-1ea3-4a58-8d6d-fa3535ca0379" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryNet_3d4fc7f3-ebfc-463d-8c99-c178cd2f281e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InventoryNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_83a969c8-1677-4a88-b1e1-5e6ecead1b18" xlink:to="loc_us-gaap_InventoryNet_3d4fc7f3-ebfc-463d-8c99-c178cd2f281e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_8df4533b-04f1-4820-8026-5f41ef06a969" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_83a969c8-1677-4a88-b1e1-5e6ecead1b18" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_8df4533b-04f1-4820-8026-5f41ef06a969" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_51b03397-56a6-4824-901f-e177fd52304c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_83a969c8-1677-4a88-b1e1-5e6ecead1b18" xlink:to="loc_us-gaap_AssetsCurrent_51b03397-56a6-4824-901f-e177fd52304c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsNoncurrentAbstract_15d9cc1f-9ec5-4962-873a-d93631dee471" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsNoncurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_4cb20fc0-6cde-4a72-980b-4b30bc9be4ce" xlink:to="loc_us-gaap_AssetsNoncurrentAbstract_15d9cc1f-9ec5-4962-873a-d93631dee471" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_6f96884f-6470-427d-90e7-3d790086548a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_15d9cc1f-9ec5-4962-873a-d93631dee471" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_6f96884f-6470-427d-90e7-3d790086548a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_d60af625-8aa7-49d1-b050-208da21a8e35" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_15d9cc1f-9ec5-4962-873a-d93631dee471" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_d60af625-8aa7-49d1-b050-208da21a8e35" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_4654b3e4-a515-4ca8-8125-0ab7c4893ba3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_15d9cc1f-9ec5-4962-873a-d93631dee471" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_4654b3e4-a515-4ca8-8125-0ab7c4893ba3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_7ba54356-34a7-48be-bd42-04e869cfe394" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_15d9cc1f-9ec5-4962-873a-d93631dee471" xlink:to="loc_us-gaap_Goodwill_7ba54356-34a7-48be-bd42-04e869cfe394" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxAssetsNet_c5dc37d8-5417-45b5-90ef-622775f7c8d0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredIncomeTaxAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_15d9cc1f-9ec5-4962-873a-d93631dee471" xlink:to="loc_us-gaap_DeferredIncomeTaxAssetsNet_c5dc37d8-5417-45b5-90ef-622775f7c8d0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_44281ec8-5d4a-45d9-99b8-97d5a7d219f4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_15d9cc1f-9ec5-4962-873a-d93631dee471" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_44281ec8-5d4a-45d9-99b8-97d5a7d219f4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsNoncurrent_f9e8ca08-937e-4948-93a0-64f64b1235aa" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_15d9cc1f-9ec5-4962-873a-d93631dee471" xlink:to="loc_us-gaap_AssetsNoncurrent_f9e8ca08-937e-4948-93a0-64f64b1235aa" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_21a8acf8-fc4d-4b61-b886-ae4cf18f0149" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_15d9cc1f-9ec5-4962-873a-d93631dee471" xlink:to="loc_us-gaap_Assets_21a8acf8-fc4d-4b61-b886-ae4cf18f0149" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_9ad9f09b-f86d-44bc-8f79-948993ec5ac6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1fe9ba7f-47c1-416e-a64a-0e88adff9705" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_9ad9f09b-f86d-44bc-8f79-948993ec5ac6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_51de842c-6a0a-45bf-8ed8-90de499dd1ce" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_9ad9f09b-f86d-44bc-8f79-948993ec5ac6" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_51de842c-6a0a-45bf-8ed8-90de499dd1ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtCurrent_9da7560a-b900-41ed-b7de-515693fc24d0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_51de842c-6a0a-45bf-8ed8-90de499dd1ce" xlink:to="loc_us-gaap_DebtCurrent_9da7560a-b900-41ed-b7de-515693fc24d0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_4452359e-f868-44d8-bd64-4dd0a1f5c44b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_51de842c-6a0a-45bf-8ed8-90de499dd1ce" xlink:to="loc_us-gaap_AccountsPayableCurrent_4452359e-f868-44d8-bd64-4dd0a1f5c44b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_42dd4ce9-4c60-4d55-bdc0-97070615a3df" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_51de842c-6a0a-45bf-8ed8-90de499dd1ce" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_42dd4ce9-4c60-4d55-bdc0-97070615a3df" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityCurrent_79a3d5f9-3bc5-447b-880d-83dbf339954e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_51de842c-6a0a-45bf-8ed8-90de499dd1ce" xlink:to="loc_us-gaap_OperatingLeaseLiabilityCurrent_79a3d5f9-3bc5-447b-880d-83dbf339954e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedIncomeTaxes_b23cfeda-e9a3-47b4-a836-666127afc8a8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccruedIncomeTaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_51de842c-6a0a-45bf-8ed8-90de499dd1ce" xlink:to="loc_us-gaap_AccruedIncomeTaxes_b23cfeda-e9a3-47b4-a836-666127afc8a8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_AccruedLiabilitiesAndOtherCurrentLiabilities_67f568f8-ebfd-48cb-ae31-b18b18bfeedd" xlink:href="gct-20231231.xsd#gct_AccruedLiabilitiesAndOtherCurrentLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_51de842c-6a0a-45bf-8ed8-90de499dd1ce" xlink:to="loc_gct_AccruedLiabilitiesAndOtherCurrentLiabilities_67f568f8-ebfd-48cb-ae31-b18b18bfeedd" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_0a966e88-dbc7-4894-b794-ce0261fdad1a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_51de842c-6a0a-45bf-8ed8-90de499dd1ce" xlink:to="loc_us-gaap_LiabilitiesCurrent_0a966e88-dbc7-4894-b794-ce0261fdad1a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesNoncurrentAbstract_c1a72339-9f6c-44c0-aa75-97f2445fb804" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesNoncurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_9ad9f09b-f86d-44bc-8f79-948993ec5ac6" xlink:to="loc_us-gaap_LiabilitiesNoncurrentAbstract_c1a72339-9f6c-44c0-aa75-97f2445fb804" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_f9f21ed8-b462-4794-89f8-b72ba8fc4f2a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_c1a72339-9f6c-44c0-aa75-97f2445fb804" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_f9f21ed8-b462-4794-89f8-b72ba8fc4f2a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_218647f8-92c4-466c-8b3b-c9e7757706b6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_c1a72339-9f6c-44c0-aa75-97f2445fb804" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_218647f8-92c4-466c-8b3b-c9e7757706b6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseLiabilityNoncurrent_4b5e9afc-a496-4fe1-86a0-d2fcfd4d42dd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FinanceLeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_c1a72339-9f6c-44c0-aa75-97f2445fb804" xlink:to="loc_us-gaap_FinanceLeaseLiabilityNoncurrent_4b5e9afc-a496-4fe1-86a0-d2fcfd4d42dd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedIncomeTaxesNoncurrent_c6915882-6afd-4e78-a366-55b4b1b518fe" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccruedIncomeTaxesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_c1a72339-9f6c-44c0-aa75-97f2445fb804" xlink:to="loc_us-gaap_AccruedIncomeTaxesNoncurrent_c6915882-6afd-4e78-a366-55b4b1b518fe" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesNoncurrent_35d187ee-1a56-4298-b5a0-5cae851fcf3d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_c1a72339-9f6c-44c0-aa75-97f2445fb804" xlink:to="loc_us-gaap_LiabilitiesNoncurrent_35d187ee-1a56-4298-b5a0-5cae851fcf3d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_09f50f76-4677-4ab7-9e9a-7b91263b0a22" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_c1a72339-9f6c-44c0-aa75-97f2445fb804" xlink:to="loc_us-gaap_Liabilities_09f50f76-4677-4ab7-9e9a-7b91263b0a22" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_195655f7-5c32-4c9e-9525-05606cbe6377" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_c1a72339-9f6c-44c0-aa75-97f2445fb804" xlink:to="loc_us-gaap_CommitmentsAndContingencies_195655f7-5c32-4c9e-9525-05606cbe6377" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityAbstract_a8172282-8840-41bd-b008-e095f11d37e4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_9ad9f09b-f86d-44bc-8f79-948993ec5ac6" xlink:to="loc_us-gaap_StockholdersEquityAbstract_a8172282-8840-41bd-b008-e095f11d37e4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockValue_91a22aeb-b4f4-432d-860a-a523238d6e11" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TreasuryStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_a8172282-8840-41bd-b008-e095f11d37e4" xlink:to="loc_us-gaap_TreasuryStockValue_91a22aeb-b4f4-432d-860a-a523238d6e11" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockShareSubscribedButUnissuedSubscriptionsReceivable_02b0cf33-1f59-481e-9e20-7e5874392eba" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockShareSubscribedButUnissuedSubscriptionsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_a8172282-8840-41bd-b008-e095f11d37e4" xlink:to="loc_us-gaap_CommonStockShareSubscribedButUnissuedSubscriptionsReceivable_02b0cf33-1f59-481e-9e20-7e5874392eba" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_c4cc955d-9544-4148-913a-57823b4a240a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_a8172282-8840-41bd-b008-e095f11d37e4" xlink:to="loc_us-gaap_CommonStockValue_c4cc955d-9544-4148-913a-57823b4a240a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapital_bb32d417-f133-47c6-8d80-97ab000bd54a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdditionalPaidInCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_a8172282-8840-41bd-b008-e095f11d37e4" xlink:to="loc_us-gaap_AdditionalPaidInCapital_bb32d417-f133-47c6-8d80-97ab000bd54a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_ccb975fa-d10c-4ada-b5bb-ff0641271b62" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_a8172282-8840-41bd-b008-e095f11d37e4" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_ccb975fa-d10c-4ada-b5bb-ff0641271b62" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_5037697e-10a0-475c-9d40-7d881b70f150" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_a8172282-8840-41bd-b008-e095f11d37e4" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_5037697e-10a0-475c-9d40-7d881b70f150" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_5d1d1b38-d5b6-4075-9405-82b09c0c6184" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_a8172282-8840-41bd-b008-e095f11d37e4" xlink:to="loc_us-gaap_StockholdersEquity_5d1d1b38-d5b6-4075-9405-82b09c0c6184" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_59133ec4-d135-445b-a5cd-20fed14e5226" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_a8172282-8840-41bd-b008-e095f11d37e4" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_59133ec4-d135-445b-a5cd-20fed14e5226" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_812fae59-3188-479d-9bf4-e5d36a43ad30" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1fe9ba7f-47c1-416e-a64a-0e88adff9705" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_812fae59-3188-479d-9bf4-e5d36a43ad30" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:type="simple" xlink:href="gct-20231231.xsd#ConsolidatedBalanceSheetsParenthetical"/>
  <link:definitionLink xlink:role="http://gig.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_1411bbda-4b1d-4108-bc55-c8e02450ef73" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_2e13c99f-a1e7-4e6c-9a0e-dd1b338438da" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_1411bbda-4b1d-4108-bc55-c8e02450ef73" xlink:to="loc_us-gaap_StatementTable_2e13c99f-a1e7-4e6c-9a0e-dd1b338438da" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_83c6963e-bbb4-47b8-9191-42cf44c40b36" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_2e13c99f-a1e7-4e6c-9a0e-dd1b338438da" xlink:to="loc_srt_ConsolidatedEntitiesAxis_83c6963e-bbb4-47b8-9191-42cf44c40b36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_83c6963e-bbb4-47b8-9191-42cf44c40b36_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_83c6963e-bbb4-47b8-9191-42cf44c40b36" xlink:to="loc_srt_ConsolidatedEntitiesDomain_83c6963e-bbb4-47b8-9191-42cf44c40b36_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01be5593-23f1-43be-bba7-845af053a3a7" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_83c6963e-bbb4-47b8-9191-42cf44c40b36" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01be5593-23f1-43be-bba7-845af053a3a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_914f8498-9cc7-448e-bd82-7a10be8663e4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_VariableInterestEntityPrimaryBeneficiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_01be5593-23f1-43be-bba7-845af053a3a7" xlink:to="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_914f8498-9cc7-448e-bd82-7a10be8663e4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_f9b183b5-a02a-44d6-9d36-343287ecd54c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_2e13c99f-a1e7-4e6c-9a0e-dd1b338438da" xlink:to="loc_us-gaap_StatementClassOfStockAxis_f9b183b5-a02a-44d6-9d36-343287ecd54c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_f9b183b5-a02a-44d6-9d36-343287ecd54c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_f9b183b5-a02a-44d6-9d36-343287ecd54c" xlink:to="loc_us-gaap_ClassOfStockDomain_f9b183b5-a02a-44d6-9d36-343287ecd54c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_884dbb30-5b0f-4e8e-b8d1-31d20e0ee77d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_f9b183b5-a02a-44d6-9d36-343287ecd54c" xlink:to="loc_us-gaap_ClassOfStockDomain_884dbb30-5b0f-4e8e-b8d1-31d20e0ee77d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_ce832fed-fdf8-4b24-8b01-37a2d8561ee2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_884dbb30-5b0f-4e8e-b8d1-31d20e0ee77d" xlink:to="loc_us-gaap_CommonClassAMember_ce832fed-fdf8-4b24-8b01-37a2d8561ee2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_709423bd-ce6f-4506-b20c-2e9cad77561a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_884dbb30-5b0f-4e8e-b8d1-31d20e0ee77d" xlink:to="loc_us-gaap_CommonClassBMember_709423bd-ce6f-4506-b20c-2e9cad77561a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_4ab88102-857c-43bf-b924-47c6e380dd3a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1411bbda-4b1d-4108-bc55-c8e02450ef73" xlink:to="loc_us-gaap_AccountsPayableCurrent_4ab88102-857c-43bf-b924-47c6e380dd3a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_604de9b8-43a1-42c6-b3ea-17e429045f72" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1411bbda-4b1d-4108-bc55-c8e02450ef73" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_604de9b8-43a1-42c6-b3ea-17e429045f72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityCurrent_cba4009f-66c5-45e4-91a6-fe17927f77a3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1411bbda-4b1d-4108-bc55-c8e02450ef73" xlink:to="loc_us-gaap_OperatingLeaseLiabilityCurrent_cba4009f-66c5-45e4-91a6-fe17927f77a3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedIncomeTaxes_5c6526bf-751e-4602-a63a-533086b2039c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccruedIncomeTaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1411bbda-4b1d-4108-bc55-c8e02450ef73" xlink:to="loc_us-gaap_AccruedIncomeTaxes_5c6526bf-751e-4602-a63a-533086b2039c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_AccruedLiabilitiesAndOtherCurrentLiabilities_9f2948c7-88cf-4244-8da7-fd0caeb446a4" xlink:href="gct-20231231.xsd#gct_AccruedLiabilitiesAndOtherCurrentLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1411bbda-4b1d-4108-bc55-c8e02450ef73" xlink:to="loc_gct_AccruedLiabilitiesAndOtherCurrentLiabilities_9f2948c7-88cf-4244-8da7-fd0caeb446a4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_d8c0b773-5699-48a2-94d1-c03a36709380" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1411bbda-4b1d-4108-bc55-c8e02450ef73" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_d8c0b773-5699-48a2-94d1-c03a36709380" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_a9e764a2-de2c-4b2c-b84a-258a9ddcf17e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TreasuryStockCommonShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1411bbda-4b1d-4108-bc55-c8e02450ef73" xlink:to="loc_us-gaap_TreasuryStockCommonShares_a9e764a2-de2c-4b2c-b84a-258a9ddcf17e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_5e7a11f4-f777-4e00-91ed-88e66deb3b10" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1411bbda-4b1d-4108-bc55-c8e02450ef73" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_5e7a11f4-f777-4e00-91ed-88e66deb3b10" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_66686b7b-76be-4d08-a9d5-26104c7d7dcc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1411bbda-4b1d-4108-bc55-c8e02450ef73" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_66686b7b-76be-4d08-a9d5-26104c7d7dcc" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_64d95d14-8f86-4ea4-8565-79fc7fdafcde" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1411bbda-4b1d-4108-bc55-c8e02450ef73" xlink:to="loc_us-gaap_CommonStockSharesIssued_64d95d14-8f86-4ea4-8565-79fc7fdafcde" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_00a38eec-0762-47e6-a93e-0a6ce546f043" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1411bbda-4b1d-4108-bc55-c8e02450ef73" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_00a38eec-0762-47e6-a93e-0a6ce546f043" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/ConsolidatedStatementsOfComprehensiveIncome" xlink:type="simple" xlink:href="gct-20231231.xsd#ConsolidatedStatementsOfComprehensiveIncome"/>
  <link:definitionLink xlink:role="http://gig.com/role/ConsolidatedStatementsOfComprehensiveIncome" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_ed28688f-ca8f-44e9-ae56-e8035f4de3a5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_7bb80cde-a407-429d-99e4-752fb3e998ac" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_ed28688f-ca8f-44e9-ae56-e8035f4de3a5" xlink:to="loc_us-gaap_StatementTable_7bb80cde-a407-429d-99e4-752fb3e998ac" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_f96b0a42-2bb5-45e2-9688-f5bdb4ee683f" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_7bb80cde-a407-429d-99e4-752fb3e998ac" xlink:to="loc_srt_ProductOrServiceAxis_f96b0a42-2bb5-45e2-9688-f5bdb4ee683f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_f96b0a42-2bb5-45e2-9688-f5bdb4ee683f_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_f96b0a42-2bb5-45e2-9688-f5bdb4ee683f" xlink:to="loc_srt_ProductsAndServicesDomain_f96b0a42-2bb5-45e2-9688-f5bdb4ee683f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_308d7fa8-f2d0-4ffe-a562-2713bff659df" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_f96b0a42-2bb5-45e2-9688-f5bdb4ee683f" xlink:to="loc_srt_ProductsAndServicesDomain_308d7fa8-f2d0-4ffe-a562-2713bff659df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServiceMember_4995e191-6c5f-4749-898c-1ccbc3c0cf4d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_308d7fa8-f2d0-4ffe-a562-2713bff659df" xlink:to="loc_us-gaap_ServiceMember_4995e191-6c5f-4749-898c-1ccbc3c0cf4d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_f3910e3f-0e1f-47de-a282-444acba851c5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_308d7fa8-f2d0-4ffe-a562-2713bff659df" xlink:to="loc_us-gaap_ProductMember_f3910e3f-0e1f-47de-a282-444acba851c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesAbstract_94ef06e0-490b-4b1e-84dd-df672b522257" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenuesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ed28688f-ca8f-44e9-ae56-e8035f4de3a5" xlink:to="loc_us-gaap_RevenuesAbstract_94ef06e0-490b-4b1e-84dd-df672b522257" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_ad6c01f9-781b-4fa8-89b6-58b97571097b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_94ef06e0-490b-4b1e-84dd-df672b522257" xlink:to="loc_us-gaap_Revenues_ad6c01f9-781b-4fa8-89b6-58b97571097b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfRevenueAbstract_5e22560b-e0e7-43da-a23a-da58939ecbe0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CostOfRevenueAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ed28688f-ca8f-44e9-ae56-e8035f4de3a5" xlink:to="loc_us-gaap_CostOfRevenueAbstract_5e22560b-e0e7-43da-a23a-da58939ecbe0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_CostOfRevenues_3f156839-c497-4205-8ae1-3639d61f491b" xlink:href="gct-20231231.xsd#gct_CostOfRevenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostOfRevenueAbstract_5e22560b-e0e7-43da-a23a-da58939ecbe0" xlink:to="loc_gct_CostOfRevenues_3f156839-c497-4205-8ae1-3639d61f491b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossProfit_4974ca10-a966-41c8-8ce4-1dedc949afaf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GrossProfit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ed28688f-ca8f-44e9-ae56-e8035f4de3a5" xlink:to="loc_us-gaap_GrossProfit_4974ca10-a966-41c8-8ce4-1dedc949afaf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpensesAbstract_60a8f611-5f98-4e0a-84b8-ee5bf3cc1b00" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ed28688f-ca8f-44e9-ae56-e8035f4de3a5" xlink:to="loc_us-gaap_OperatingExpensesAbstract_60a8f611-5f98-4e0a-84b8-ee5bf3cc1b00" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpense_d9630229-a3c1-4560-ace5-398d2782605f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SellingAndMarketingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_60a8f611-5f98-4e0a-84b8-ee5bf3cc1b00" xlink:to="loc_us-gaap_SellingAndMarketingExpense_d9630229-a3c1-4560-ace5-398d2782605f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_67f69134-dd19-42e7-bd96-0b3b9d24055b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_60a8f611-5f98-4e0a-84b8-ee5bf3cc1b00" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_67f69134-dd19-42e7-bd96-0b3b9d24055b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_40864a58-c8b6-429a-b498-fb37173815d0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_60a8f611-5f98-4e0a-84b8-ee5bf3cc1b00" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_40864a58-c8b6-429a-b498-fb37173815d0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfPropertyPlantEquipment_bb143b13-c42d-4a51-acb3-d7e46b93bca0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GainLossOnSaleOfPropertyPlantEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_60a8f611-5f98-4e0a-84b8-ee5bf3cc1b00" xlink:to="loc_us-gaap_GainLossOnSaleOfPropertyPlantEquipment_bb143b13-c42d-4a51-acb3-d7e46b93bca0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpenses_7ff5652b-8639-46a1-97b9-bfc9d1d5d1a0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_60a8f611-5f98-4e0a-84b8-ee5bf3cc1b00" xlink:to="loc_us-gaap_OperatingExpenses_7ff5652b-8639-46a1-97b9-bfc9d1d5d1a0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_5a0ca478-d471-4ec3-9a85-434868377e12" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ed28688f-ca8f-44e9-ae56-e8035f4de3a5" xlink:to="loc_us-gaap_OperatingIncomeLoss_5a0ca478-d471-4ec3-9a85-434868377e12" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpense_3c82e101-bf3e-4577-9d2b-44e5a19f7bfa" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ed28688f-ca8f-44e9-ae56-e8035f4de3a5" xlink:to="loc_us-gaap_InterestExpense_3c82e101-bf3e-4577-9d2b-44e5a19f7bfa" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnInvestments_ee8e2ff4-ab14-45be-b296-287b0a93662a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GainLossOnInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ed28688f-ca8f-44e9-ae56-e8035f4de3a5" xlink:to="loc_us-gaap_GainLossOnInvestments_ee8e2ff4-ab14-45be-b296-287b0a93662a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyTransactionGainLossBeforeTax_46f3cec2-11ba-45b0-ae27-c584df4c226d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ForeignCurrencyTransactionGainLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ed28688f-ca8f-44e9-ae56-e8035f4de3a5" xlink:to="loc_us-gaap_ForeignCurrencyTransactionGainLossBeforeTax_46f3cec2-11ba-45b0-ae27-c584df4c226d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_IncomeFromGovernmentGrants_b9a8a828-65cb-478c-8ad4-7a52cf819374" xlink:href="gct-20231231.xsd#gct_IncomeFromGovernmentGrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ed28688f-ca8f-44e9-ae56-e8035f4de3a5" xlink:to="loc_gct_IncomeFromGovernmentGrants_b9a8a828-65cb-478c-8ad4-7a52cf819374" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_25df680e-a018-4d7c-8938-9fee22842cee" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ed28688f-ca8f-44e9-ae56-e8035f4de3a5" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_25df680e-a018-4d7c-8938-9fee22842cee" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_06f30815-7b38-447a-9d31-a56d5575a2aa" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ed28688f-ca8f-44e9-ae56-e8035f4de3a5" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_06f30815-7b38-447a-9d31-a56d5575a2aa" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_f023fc0b-b2f7-4f74-aaae-8419110ffa04" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ed28688f-ca8f-44e9-ae56-e8035f4de3a5" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_f023fc0b-b2f7-4f74-aaae-8419110ffa04" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_7d8a15d6-73a0-4a91-9283-da9ec54f39b6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ed28688f-ca8f-44e9-ae56-e8035f4de3a5" xlink:to="loc_us-gaap_NetIncomeLoss_7d8a15d6-73a0-4a91-9283-da9ec54f39b6" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment_daac8cd3-2db4-4e4a-9cbd-9f1ba818cc58" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ed28688f-ca8f-44e9-ae56-e8035f4de3a5" xlink:to="loc_us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment_daac8cd3-2db4-4e4a-9cbd-9f1ba818cc58" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_6692e08f-7057-48fa-a04f-f0dcbac3057e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ed28688f-ca8f-44e9-ae56-e8035f4de3a5" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_6692e08f-7057-48fa-a04f-f0dcbac3057e" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_90d276b7-ce2c-4a1e-98d2-b57965aa24ec" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ed28688f-ca8f-44e9-ae56-e8035f4de3a5" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_90d276b7-ce2c-4a1e-98d2-b57965aa24ec" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_896c3a66-9b5d-4348-972d-1e56eb3d73bf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ed28688f-ca8f-44e9-ae56-e8035f4de3a5" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_896c3a66-9b5d-4348-972d-1e56eb3d73bf" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_53023191-c162-4b19-9088-1fad8150330e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ed28688f-ca8f-44e9-ae56-e8035f4de3a5" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_53023191-c162-4b19-9088-1fad8150330e" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareAbstract_8cf6eee2-2faf-4d66-a9ef-6279d87dfb2b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EarningsPerShareAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ed28688f-ca8f-44e9-ae56-e8035f4de3a5" xlink:to="loc_us-gaap_EarningsPerShareAbstract_8cf6eee2-2faf-4d66-a9ef-6279d87dfb2b" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_134a461c-0201-4373-b28e-881685133fd3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_8cf6eee2-2faf-4d66-a9ef-6279d87dfb2b" xlink:to="loc_us-gaap_EarningsPerShareBasic_134a461c-0201-4373-b28e-881685133fd3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_e0e8c99a-b72e-4f41-8671-0a2ee82dc974" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_8cf6eee2-2faf-4d66-a9ef-6279d87dfb2b" xlink:to="loc_us-gaap_EarningsPerShareDiluted_e0e8c99a-b72e-4f41-8671-0a2ee82dc974" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract_cce9077b-e708-4de5-9783-92ed19ef9325" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ed28688f-ca8f-44e9-ae56-e8035f4de3a5" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract_cce9077b-e708-4de5-9783-92ed19ef9325" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_b7a51f32-4f42-4af2-93a4-6a2154c53105" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract_cce9077b-e708-4de5-9783-92ed19ef9325" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_b7a51f32-4f42-4af2-93a4-6a2154c53105" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_66478f8e-47bc-47fc-9eea-3214e53bb4ec" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract_cce9077b-e708-4de5-9783-92ed19ef9325" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_66478f8e-47bc-47fc-9eea-3214e53bb4ec" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity" xlink:type="simple" xlink:href="gct-20231231.xsd#ConsolidatedStatementsOfChangesInShareholdersEquity"/>
  <link:definitionLink xlink:role="http://gig.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_b37b81ad-e3f4-46bf-9252-b85cf3e1b419" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:to="loc_us-gaap_StatementTable_b37b81ad-e3f4-46bf-9252-b85cf3e1b419" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_713e6b80-9bb5-47b9-b35c-523eb134337c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_b37b81ad-e3f4-46bf-9252-b85cf3e1b419" xlink:to="loc_us-gaap_StatementClassOfStockAxis_713e6b80-9bb5-47b9-b35c-523eb134337c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_713e6b80-9bb5-47b9-b35c-523eb134337c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_713e6b80-9bb5-47b9-b35c-523eb134337c" xlink:to="loc_us-gaap_ClassOfStockDomain_713e6b80-9bb5-47b9-b35c-523eb134337c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_20b0f7c3-36af-4452-bd8f-aaa0a728de07" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_713e6b80-9bb5-47b9-b35c-523eb134337c" xlink:to="loc_us-gaap_ClassOfStockDomain_20b0f7c3-36af-4452-bd8f-aaa0a728de07" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_4d37a7c8-2f60-4f0b-b29d-da34196a1475" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_20b0f7c3-36af-4452-bd8f-aaa0a728de07" xlink:to="loc_us-gaap_CommonClassAMember_4d37a7c8-2f60-4f0b-b29d-da34196a1475" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_a6515e73-4161-4794-acf9-585f0402fd4e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_20b0f7c3-36af-4452-bd8f-aaa0a728de07" xlink:to="loc_us-gaap_CommonClassBMember_a6515e73-4161-4794-acf9-585f0402fd4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ClassAOrdinarySharesMember_fc83d600-b4f4-4ff8-b28c-dceecffce42f" xlink:href="gct-20231231.xsd#gct_ClassAOrdinarySharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_20b0f7c3-36af-4452-bd8f-aaa0a728de07" xlink:to="loc_gct_ClassAOrdinarySharesMember_fc83d600-b4f4-4ff8-b28c-dceecffce42f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ClassBOrdinarySharesMember_9cd81925-3529-454d-a6f4-df553a39675b" xlink:href="gct-20231231.xsd#gct_ClassBOrdinarySharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_20b0f7c3-36af-4452-bd8f-aaa0a728de07" xlink:to="loc_gct_ClassBOrdinarySharesMember_9cd81925-3529-454d-a6f4-df553a39675b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_ef6690a7-d07e-4615-bcc8-984d32b6c27e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_b37b81ad-e3f4-46bf-9252-b85cf3e1b419" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_ef6690a7-d07e-4615-bcc8-984d32b6c27e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_ef6690a7-d07e-4615-bcc8-984d32b6c27e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_ef6690a7-d07e-4615-bcc8-984d32b6c27e" xlink:to="loc_us-gaap_EquityComponentDomain_ef6690a7-d07e-4615-bcc8-984d32b6c27e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_7334a8b3-d965-444f-baef-7d5a71bdc684" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_ef6690a7-d07e-4615-bcc8-984d32b6c27e" xlink:to="loc_us-gaap_EquityComponentDomain_7334a8b3-d965-444f-baef-7d5a71bdc684" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_a0f0336b-569f-48ba-8464-7f97f8aae2ef" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_7334a8b3-d965-444f-baef-7d5a71bdc684" xlink:to="loc_us-gaap_CommonStockMember_a0f0336b-569f-48ba-8464-7f97f8aae2ef" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_c78618e8-13bf-4d2f-b00e-703cee15e09d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_7334a8b3-d965-444f-baef-7d5a71bdc684" xlink:to="loc_us-gaap_TreasuryStockCommonMember_c78618e8-13bf-4d2f-b00e-703cee15e09d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_SubscriptionReceivableFromOrdinarySharesMember_74f3c0c7-9109-470b-960b-595368264810" xlink:href="gct-20231231.xsd#gct_SubscriptionReceivableFromOrdinarySharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_7334a8b3-d965-444f-baef-7d5a71bdc684" xlink:to="loc_gct_SubscriptionReceivableFromOrdinarySharesMember_74f3c0c7-9109-470b-960b-595368264810" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockMember_fede9897-9bb8-416a-b78f-1e363703f39a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_7334a8b3-d965-444f-baef-7d5a71bdc684" xlink:to="loc_us-gaap_PreferredStockMember_fede9897-9bb8-416a-b78f-1e363703f39a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_687f3663-fe49-4f1f-9ccc-43d60e76f34a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_7334a8b3-d965-444f-baef-7d5a71bdc684" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_687f3663-fe49-4f1f-9ccc-43d60e76f34a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_c89a7f81-f14e-4a54-8bb0-a0f6646c00d8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_7334a8b3-d965-444f-baef-7d5a71bdc684" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_c89a7f81-f14e-4a54-8bb0-a0f6646c00d8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_9440f316-fb9a-40c2-aec2-f21ba0a48449" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_7334a8b3-d965-444f-baef-7d5a71bdc684" xlink:to="loc_us-gaap_RetainedEarningsMember_9440f316-fb9a-40c2-aec2-f21ba0a48449" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_9c3c80ca-3900-4582-80e8-45441c814517" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConversionOfStockByUniqueDescriptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_b37b81ad-e3f4-46bf-9252-b85cf3e1b419" xlink:to="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_9c3c80ca-3900-4582-80e8-45441c814517" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_9c3c80ca-3900-4582-80e8-45441c814517_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConversionOfStockNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_9c3c80ca-3900-4582-80e8-45441c814517" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_9c3c80ca-3900-4582-80e8-45441c814517_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_fb55c1cb-6f8d-4b86-8945-070d7d9fa64a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConversionOfStockNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_9c3c80ca-3900-4582-80e8-45441c814517" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_fb55c1cb-6f8d-4b86-8945-070d7d9fa64a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ConversionOfPreferredSharesToClassBOrdinarySharesMember_ef7a9724-6190-4716-92ac-01e580fb585d" xlink:href="gct-20231231.xsd#gct_ConversionOfPreferredSharesToClassBOrdinarySharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_fb55c1cb-6f8d-4b86-8945-070d7d9fa64a" xlink:to="loc_gct_ConversionOfPreferredSharesToClassBOrdinarySharesMember_ef7a9724-6190-4716-92ac-01e580fb585d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ConversionOfPreferredSharesToClassAOrdinarySharesMember_fa3aaf0a-5f27-41b1-b702-026704b699e1" xlink:href="gct-20231231.xsd#gct_ConversionOfPreferredSharesToClassAOrdinarySharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_fb55c1cb-6f8d-4b86-8945-070d7d9fa64a" xlink:to="loc_gct_ConversionOfPreferredSharesToClassAOrdinarySharesMember_fa3aaf0a-5f27-41b1-b702-026704b699e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ConversionOfSeriesEPreferredSharesToClassAOrdinarySharesMember_fcce7573-af52-4042-ac73-3976bd8bf3c7" xlink:href="gct-20231231.xsd#gct_ConversionOfSeriesEPreferredSharesToClassAOrdinarySharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_fb55c1cb-6f8d-4b86-8945-070d7d9fa64a" xlink:to="loc_gct_ConversionOfSeriesEPreferredSharesToClassAOrdinarySharesMember_fcce7573-af52-4042-ac73-3976bd8bf3c7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_2eb24cf1-7db9-4984-a975-6d5d0af1bd7c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_b37b81ad-e3f4-46bf-9252-b85cf3e1b419" xlink:to="loc_us-gaap_AwardTypeAxis_2eb24cf1-7db9-4984-a975-6d5d0af1bd7c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2eb24cf1-7db9-4984-a975-6d5d0af1bd7c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_2eb24cf1-7db9-4984-a975-6d5d0af1bd7c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2eb24cf1-7db9-4984-a975-6d5d0af1bd7c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_af9bfcfb-0a0c-4d04-bf17-2f1d4e8ca7de" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_2eb24cf1-7db9-4984-a975-6d5d0af1bd7c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_af9bfcfb-0a0c-4d04-bf17-2f1d4e8ca7de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_86573738-b91c-4636-9528-3acf12b9dfb3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_af9bfcfb-0a0c-4d04-bf17-2f1d4e8ca7de" xlink:to="loc_us-gaap_RestrictedStockMember_86573738-b91c-4636-9528-3acf12b9dfb3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_e1ee7407-e758-47f0-857e-d17f41d7d4e5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:to="loc_us-gaap_SharesOutstanding_e1ee7407-e758-47f0-857e-d17f41d7d4e5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_08b20b02-f3c5-4d80-bc4f-2625e228ab66" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_08b20b02-f3c5-4d80-bc4f-2625e228ab66" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_52779df8-7ddf-4e62-9e2d-c1b9d0d3d205" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:to="loc_us-gaap_NetIncomeLoss_52779df8-7ddf-4e62-9e2d-c1b9d0d3d205" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_eb4840ca-054f-4c28-a4f2-35723dfa8c94" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_eb4840ca-054f-4c28-a4f2-35723dfa8c94" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_48af019a-1537-4506-ab34-5738332e1a35" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_48af019a-1537-4506-ab34-5738332e1a35" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_c8e61b2f-0c4c-4b6d-abd1-0f824e50dff4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_c8e61b2f-0c4c-4b6d-abd1-0f824e50dff4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseInCarryingAmountOfRedeemablePreferredStock_2ecbc7ed-ed15-4ff8-a7ca-bc0a9e3f3b4a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseInCarryingAmountOfRedeemablePreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:to="loc_us-gaap_IncreaseInCarryingAmountOfRedeemablePreferredStock_2ecbc7ed-ed15-4ff8-a7ca-bc0a9e3f3b4a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesIssuedForServices_c48c9312-c453-4127-b595-bfd2f623e26e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesIssuedForServices"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesIssuedForServices_c48c9312-c453-4127-b595-bfd2f623e26e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueIssuedForServices_73b3f05a-6ce8-4b9c-8cf5-114990cd059f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodValueIssuedForServices"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueIssuedForServices_73b3f05a-6ce8-4b9c-8cf5-114990cd059f" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_StockIssuedDuringPeriodSharesIssuedForTrustHoldcos_f199e8ec-29a9-4ae5-a500-789854e29c2d" xlink:href="gct-20231231.xsd#gct_StockIssuedDuringPeriodSharesIssuedForTrustHoldcos"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:to="loc_gct_StockIssuedDuringPeriodSharesIssuedForTrustHoldcos_f199e8ec-29a9-4ae5-a500-789854e29c2d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_StockIssuedDuringPeriodValueIssuedForTrustHoldcos_333fc142-756e-4794-badb-8e2ce4406f63" xlink:href="gct-20231231.xsd#gct_StockIssuedDuringPeriodValueIssuedForTrustHoldcos"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:to="loc_gct_StockIssuedDuringPeriodValueIssuedForTrustHoldcos_333fc142-756e-4794-badb-8e2ce4406f63" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_f4b43ae2-9ff5-43f6-b3e1-3922927a222c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_f4b43ae2-9ff5-43f6-b3e1-3922927a222c" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_164fdb95-a71c-4b39-b16c-0137793aa954" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_164fdb95-a71c-4b39-b16c-0137793aa954" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockSharesConverted1_a7d89419-b83b-4661-834f-74f183b6d891" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConversionOfStockSharesConverted1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:to="loc_us-gaap_ConversionOfStockSharesConverted1_a7d89419-b83b-4661-834f-74f183b6d891" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockAmountConverted1_73c77573-15ab-431f-b91d-45e2b2de2309" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConversionOfStockAmountConverted1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:to="loc_us-gaap_ConversionOfStockAmountConverted1_73c77573-15ab-431f-b91d-45e2b2de2309" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits_d9a9a1f0-84b9-4fa8-a3ed-abe0114f2aa6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits_d9a9a1f0-84b9-4fa8-a3ed-abe0114f2aa6" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfUnits_84d086ed-60e1-4316-acd0-347e9fabbb81" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodValueConversionOfUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfUnits_84d086ed-60e1-4316-acd0-347e9fabbb81" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesPurchasedForAward_cb683288-bbb1-4b2a-8b7b-32e0f8c7b6a9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesPurchasedForAward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesPurchasedForAward_cb683288-bbb1-4b2a-8b7b-32e0f8c7b6a9" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesPurchasedForAwardValue_04fa39e1-5dab-4ab4-b162-8b4925f70a38" xlink:href="gct-20231231.xsd#gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesPurchasedForAwardValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:to="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesPurchasedForAwardValue_04fa39e1-5dab-4ab4-b162-8b4925f70a38" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_1dc9d195-9d7b-4ba8-95e9-9154e73ce293" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_1dc9d195-9d7b-4ba8-95e9-9154e73ce293" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockSharesAcquired_2f87982e-ad6c-49df-bef8-c4df290fcec4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TreasuryStockSharesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:to="loc_us-gaap_TreasuryStockSharesAcquired_2f87982e-ad6c-49df-bef8-c4df290fcec4" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_7a0f02a5-8f2f-4ad1-b0da-9f17f64afd2d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TreasuryStockValueAcquiredCostMethod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:to="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_7a0f02a5-8f2f-4ad1-b0da-9f17f64afd2d" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_471ae463-6ae4-4824-bb2e-1ad24e267deb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7486c7ac-7fd7-4a1e-9505-cba4b6d15ae1" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_471ae463-6ae4-4824-bb2e-1ad24e267deb" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_ce892289-075f-4d4b-9169-608f87a0c8d8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_74664674-4c02-4f4a-8537-6c8dc191e6a2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/DescriptionofBusinessandOrganizationScheduleofConsolidatedAssetsandLiabilitiesInformationofGroupVariableInterestEntityDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#DescriptionofBusinessandOrganizationScheduleofConsolidatedAssetsandLiabilitiesInformationofGroupVariableInterestEntityDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/DescriptionofBusinessandOrganizationScheduleofConsolidatedAssetsandLiabilitiesInformationofGroupVariableInterestEntityDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:href="gct-20231231.xsd#gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityTable_abf18706-ad17-4585-8658-8b1d19832dac" xlink:href="gct-20231231.xsd#gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityTable_abf18706-ad17-4585-8658-8b1d19832dac" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_5cdfbfd6-8141-4ab5-8f4b-a550da9e4b86" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityTable_abf18706-ad17-4585-8658-8b1d19832dac" xlink:to="loc_srt_ConsolidatedEntitiesAxis_5cdfbfd6-8141-4ab5-8f4b-a550da9e4b86" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_5cdfbfd6-8141-4ab5-8f4b-a550da9e4b86_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_5cdfbfd6-8141-4ab5-8f4b-a550da9e4b86" xlink:to="loc_srt_ConsolidatedEntitiesDomain_5cdfbfd6-8141-4ab5-8f4b-a550da9e4b86_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_9e76f690-2c57-475a-a481-8abae2dc13ae" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_5cdfbfd6-8141-4ab5-8f4b-a550da9e4b86" xlink:to="loc_srt_ConsolidatedEntitiesDomain_9e76f690-2c57-475a-a481-8abae2dc13ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_e4f3f615-8c03-4fea-85fa-2f9ed04442b5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_VariableInterestEntityPrimaryBeneficiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_9e76f690-2c57-475a-a481-8abae2dc13ae" xlink:to="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_e4f3f615-8c03-4fea-85fa-2f9ed04442b5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_c95ce6cb-ea3d-421a-86d1-911554813918" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityTable_abf18706-ad17-4585-8658-8b1d19832dac" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_c95ce6cb-ea3d-421a-86d1-911554813918" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_c95ce6cb-ea3d-421a-86d1-911554813918_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_c95ce6cb-ea3d-421a-86d1-911554813918" xlink:to="loc_us-gaap_RelatedPartyDomain_c95ce6cb-ea3d-421a-86d1-911554813918_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_1469aab8-3a10-4aeb-bf0a-c080babd45ec" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_c95ce6cb-ea3d-421a-86d1-911554813918" xlink:to="loc_us-gaap_RelatedPartyDomain_1469aab8-3a10-4aeb-bf0a-c080babd45ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrelatedPartyMember_d3a797e4-a673-4ca5-9a29-fe7a059c9811" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NonrelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_1469aab8-3a10-4aeb-bf0a-c080babd45ec" xlink:to="loc_us-gaap_NonrelatedPartyMember_d3a797e4-a673-4ca5-9a29-fe7a059c9811" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_2e19bd8a-37b5-41b8-947d-b0bf651f8071" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_1469aab8-3a10-4aeb-bf0a-c080babd45ec" xlink:to="loc_us-gaap_RelatedPartyMember_2e19bd8a-37b5-41b8-947d-b0bf651f8071" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_8e7a47a5-61ac-43c1-aa9a-e7d20b7f9de6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_8e7a47a5-61ac-43c1-aa9a-e7d20b7f9de6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_964db5a1-a4ab-4e83-b83f-f3be3d7bb589" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_964db5a1-a4ab-4e83-b83f-f3be3d7bb589" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryNet_b48d2bd8-9e23-4900-a8c9-1fab37fa0656" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InventoryNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_us-gaap_InventoryNet_b48d2bd8-9e23-4900-a8c9-1fab37fa0656" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherReceivablesNetCurrent_f28b7ddb-208b-4ff5-beeb-c7a8d7decad7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherReceivablesNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_us-gaap_OtherReceivablesNetCurrent_f28b7ddb-208b-4ff5-beeb-c7a8d7decad7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_94d33775-6be9-4606-a65b-55628525f9dc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_94d33775-6be9-4606-a65b-55628525f9dc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_87639e45-ed59-4094-ad65-55fef0f3d9fa" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_us-gaap_AssetsCurrent_87639e45-ed59-4094-ad65-55fef0f3d9fa" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_e49f8a80-e875-4bf7-af13-71f24c287b0c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_e49f8a80-e875-4bf7-af13-71f24c287b0c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_f83fc5fa-8de5-4373-b205-56e39436101d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_f83fc5fa-8de5-4373-b205-56e39436101d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_c8b7381d-a8af-4087-98c2-fc0eb4e4446f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_c8b7381d-a8af-4087-98c2-fc0eb4e4446f" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_dd2ba5ac-608a-4001-90bf-55f39e626576" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_us-gaap_Assets_dd2ba5ac-608a-4001-90bf-55f39e626576" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrentAndNoncurrent_d014fc04-ba3a-48c9-87f4-e2ea8b4e2dba" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccountsPayableCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_us-gaap_AccountsPayableCurrentAndNoncurrent_d014fc04-ba3a-48c9-87f4-e2ea8b4e2dba" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_f6079781-98dc-40fb-8be4-586bafc95395" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_f6079781-98dc-40fb-8be4-586bafc95395" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityCurrent_67a77c0d-97d0-440a-844f-43a6d330d44e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_us-gaap_OperatingLeaseLiabilityCurrent_67a77c0d-97d0-440a-844f-43a6d330d44e" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedIncomeTaxes_34b23000-ee04-459a-9bfe-e32e7a0a359c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccruedIncomeTaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_us-gaap_AccruedIncomeTaxes_34b23000-ee04-459a-9bfe-e32e7a0a359c" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_AccruedExpensesAndOtherCurrentLiabilities_73f78a0c-77d3-4094-9bc0-385f416e52c3" xlink:href="gct-20231231.xsd#gct_AccruedExpensesAndOtherCurrentLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_gct_AccruedExpensesAndOtherCurrentLiabilities_73f78a0c-77d3-4094-9bc0-385f416e52c3" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesCurrent_7b166004-a046-478a-84b1-6781dae86888" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_us-gaap_OtherLiabilitiesCurrent_7b166004-a046-478a-84b1-6781dae86888" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_6f0f5675-502b-425b-8054-af630ac796d7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_us-gaap_LiabilitiesCurrent_6f0f5675-502b-425b-8054-af630ac796d7" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_390870e6-ca5b-4936-8fee-2fcd849c518b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_390870e6-ca5b-4936-8fee-2fcd849c518b" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_f60bbeec-d170-4860-8ed9-ce8c49a80823" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_us-gaap_Liabilities_f60bbeec-d170-4860-8ed9-ce8c49a80823" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_b4f66903-1653-48f4-9b37-379977160835" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_us-gaap_Revenues_b4f66903-1653-48f4-9b37-379977160835" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_86721890-d2b1-4819-b363-bb007bebba76" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_us-gaap_NetIncomeLoss_86721890-d2b1-4819-b363-bb007bebba76" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_48277fda-4830-4b61-af12-0121ac106a00" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_48277fda-4830-4b61-af12-0121ac106a00" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_8f0efd19-0bcd-4e15-84a7-61a2277d7ef8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_8f0efd19-0bcd-4e15-84a7-61a2277d7ef8" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_b6990059-91da-4393-a3c5-86df4aa3e5f1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_b6990059-91da-4393-a3c5-86df4aa3e5f1" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffects_3d0b3aad-f361-4e5f-b292-97fca242c1be" xlink:href="gct-20231231.xsd#gct_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffects"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_gct_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffects_3d0b3aad-f361-4e5f-b292-97fca242c1be" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_647fac86-0332-42c2-9c56-72d2b9351d06" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_f096d17e-dc8e-4f91-9908-cdcab62d49c0" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_647fac86-0332-42c2-9c56-72d2b9351d06" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_5ecfcc98-eb16-49cf-a2a1-53c551406cef" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/DescriptionofBusinessandOrganizationAdditionalInformationDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#DescriptionofBusinessandOrganizationAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/DescriptionofBusinessandOrganizationAdditionalInformationDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_0609bbf6-d822-4555-81f6-f61d5b06e2be" xlink:href="gct-20231231.xsd#gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityTable_922811e9-050a-44be-86b0-3d552dff8a88" xlink:href="gct-20231231.xsd#gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_0609bbf6-d822-4555-81f6-f61d5b06e2be" xlink:to="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityTable_922811e9-050a-44be-86b0-3d552dff8a88" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_96da8ae3-9f39-4e66-91fe-2f2ec1afd5f6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityTable_922811e9-050a-44be-86b0-3d552dff8a88" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_96da8ae3-9f39-4e66-91fe-2f2ec1afd5f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_96da8ae3-9f39-4e66-91fe-2f2ec1afd5f6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_96da8ae3-9f39-4e66-91fe-2f2ec1afd5f6" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_96da8ae3-9f39-4e66-91fe-2f2ec1afd5f6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_e914ab6d-2cd8-4a81-b1af-5595b1ae01ee" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_96da8ae3-9f39-4e66-91fe-2f2ec1afd5f6" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_e914ab6d-2cd8-4a81-b1af-5595b1ae01ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_SuzhouGigacloudMember_a8a6b782-a0fa-46dc-bcba-de0e0d762afa" xlink:href="gct-20231231.xsd#gct_SuzhouGigacloudMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_e914ab6d-2cd8-4a81-b1af-5595b1ae01ee" xlink:to="loc_gct_SuzhouGigacloudMember_a8a6b782-a0fa-46dc-bcba-de0e0d762afa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_GigaCloudLogisticsIncAndBlitzDistributionGmbhMember_3b305176-52dd-42f8-8835-0007a513b840" xlink:href="gct-20231231.xsd#gct_GigaCloudLogisticsIncAndBlitzDistributionGmbhMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_e914ab6d-2cd8-4a81-b1af-5595b1ae01ee" xlink:to="loc_gct_GigaCloudLogisticsIncAndBlitzDistributionGmbhMember_3b305176-52dd-42f8-8835-0007a513b840" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_549e9e31-00cc-4714-834e-2c8a853ef5d8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_0609bbf6-d822-4555-81f6-f61d5b06e2be" xlink:to="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_549e9e31-00cc-4714-834e-2c8a853ef5d8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_NumberOfAccountControlAgreementsTerminated_bc643594-99ce-49d1-962c-63c18ee959e4" xlink:href="gct-20231231.xsd#gct_NumberOfAccountControlAgreementsTerminated"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_0609bbf6-d822-4555-81f6-f61d5b06e2be" xlink:to="loc_gct_NumberOfAccountControlAgreementsTerminated_bc643594-99ce-49d1-962c-63c18ee959e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_NumberOfWhollyOwnedSubsidiariesAcquired_a729f9d1-09c2-4db9-bab7-9dfde9b2130d" xlink:href="gct-20231231.xsd#gct_NumberOfWhollyOwnedSubsidiariesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfConsolidatedBalanceSheetsIncomeStatementAndCashFlowsOfVariableInterestEntityLineItems_0609bbf6-d822-4555-81f6-f61d5b06e2be" xlink:to="loc_gct_NumberOfWhollyOwnedSubsidiariesAcquired_a729f9d1-09c2-4db9-bab7-9dfde9b2130d" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/SummaryofSignificantAccountingPoliciesSummaryofCashDepositedDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#SummaryofSignificantAccountingPoliciesSummaryofCashDepositedDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/SummaryofSignificantAccountingPoliciesSummaryofCashDepositedDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_d4443c56-a6c8-4ba3-9939-44c1a43e73d2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_8786a247-0f42-4e17-a98f-537ada4de11f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_d4443c56-a6c8-4ba3-9939-44c1a43e73d2" xlink:to="loc_us-gaap_StatementTable_8786a247-0f42-4e17-a98f-537ada4de11f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_c7a4eb92-e77a-4283-a15e-e97f9e25f47f" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_8786a247-0f42-4e17-a98f-537ada4de11f" xlink:to="loc_srt_StatementGeographicalAxis_c7a4eb92-e77a-4283-a15e-e97f9e25f47f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_c7a4eb92-e77a-4283-a15e-e97f9e25f47f_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_c7a4eb92-e77a-4283-a15e-e97f9e25f47f" xlink:to="loc_srt_SegmentGeographicalDomain_c7a4eb92-e77a-4283-a15e-e97f9e25f47f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_58686416-731d-41c3-8dc0-b2d1e9a7f74c" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_c7a4eb92-e77a-4283-a15e-e97f9e25f47f" xlink:to="loc_srt_SegmentGeographicalDomain_58686416-731d-41c3-8dc0-b2d1e9a7f74c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_f0ed0e23-d7a9-4e08-9cfe-927c2dfd0c01" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_58686416-731d-41c3-8dc0-b2d1e9a7f74c" xlink:to="loc_country_US_f0ed0e23-d7a9-4e08-9cfe-927c2dfd0c01" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_HK_ba44a7f8-f742-4611-89fe-d8a1ac2eb089" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_HK"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_58686416-731d-41c3-8dc0-b2d1e9a7f74c" xlink:to="loc_country_HK_ba44a7f8-f742-4611-89fe-d8a1ac2eb089" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_JP_e0598863-98d9-4c89-b974-f048deb9a56e" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_JP"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_58686416-731d-41c3-8dc0-b2d1e9a7f74c" xlink:to="loc_country_JP_e0598863-98d9-4c89-b974-f048deb9a56e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_GB_7b9ee9f8-af46-4550-a481-efd76a5006e3" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_GB"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_58686416-731d-41c3-8dc0-b2d1e9a7f74c" xlink:to="loc_country_GB_7b9ee9f8-af46-4550-a481-efd76a5006e3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_CN_0157cd43-7af6-4507-8cdc-b02b556b2e65" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_CN"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_58686416-731d-41c3-8dc0-b2d1e9a7f74c" xlink:to="loc_country_CN_0157cd43-7af6-4507-8cdc-b02b556b2e65" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_DE_0d6bfc99-4423-45eb-bfac-206d4550512a" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_DE"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_58686416-731d-41c3-8dc0-b2d1e9a7f74c" xlink:to="loc_country_DE_0d6bfc99-4423-45eb-bfac-206d4550512a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_VN_4eb2ffb0-2cab-4544-a0a3-07f6644a7989" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_VN"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_58686416-731d-41c3-8dc0-b2d1e9a7f74c" xlink:to="loc_country_VN_4eb2ffb0-2cab-4544-a0a3-07f6644a7989" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_MY_13ab7436-9b19-4755-a7cc-93eb313fc3be" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_MY"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_58686416-731d-41c3-8dc0-b2d1e9a7f74c" xlink:to="loc_country_MY_13ab7436-9b19-4755-a7cc-93eb313fc3be" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CurrencyAxis_4865b1b6-0128-49eb-ace6-c87a4010ea8b" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CurrencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_8786a247-0f42-4e17-a98f-537ada4de11f" xlink:to="loc_srt_CurrencyAxis_4865b1b6-0128-49eb-ace6-c87a4010ea8b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_AllCurrenciesDomain_4865b1b6-0128-49eb-ace6-c87a4010ea8b_default" xlink:href="https://xbrl.sec.gov/currency/2023/currency-2023.xsd#currency_AllCurrenciesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CurrencyAxis_4865b1b6-0128-49eb-ace6-c87a4010ea8b" xlink:to="loc_currency_AllCurrenciesDomain_4865b1b6-0128-49eb-ace6-c87a4010ea8b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_AllCurrenciesDomain_803ce861-ad90-4010-8681-f9883cfd2464" xlink:href="https://xbrl.sec.gov/currency/2023/currency-2023.xsd#currency_AllCurrenciesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CurrencyAxis_4865b1b6-0128-49eb-ace6-c87a4010ea8b" xlink:to="loc_currency_AllCurrenciesDomain_803ce861-ad90-4010-8681-f9883cfd2464" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_USD_df30bc34-0335-4b97-9b2f-f99c20b7708f" xlink:href="https://xbrl.sec.gov/currency/2023/currency-2023.xsd#currency_USD"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_803ce861-ad90-4010-8681-f9883cfd2464" xlink:to="loc_currency_USD_df30bc34-0335-4b97-9b2f-f99c20b7708f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_EUR_eff8c147-a96e-42ee-a3a1-fb54a94e8533" xlink:href="https://xbrl.sec.gov/currency/2023/currency-2023.xsd#currency_EUR"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_803ce861-ad90-4010-8681-f9883cfd2464" xlink:to="loc_currency_EUR_eff8c147-a96e-42ee-a3a1-fb54a94e8533" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_GBP_3934b825-187b-4ee2-86eb-3cd209ef71b1" xlink:href="https://xbrl.sec.gov/currency/2023/currency-2023.xsd#currency_GBP"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_803ce861-ad90-4010-8681-f9883cfd2464" xlink:to="loc_currency_GBP_3934b825-187b-4ee2-86eb-3cd209ef71b1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_CAD_9dead933-4fa3-458d-a030-8497312a6bed" xlink:href="https://xbrl.sec.gov/currency/2023/currency-2023.xsd#currency_CAD"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_803ce861-ad90-4010-8681-f9883cfd2464" xlink:to="loc_currency_CAD_9dead933-4fa3-458d-a030-8497312a6bed" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_MXN_f3814cb3-f1bc-49f6-9875-1dd54974d4c9" xlink:href="https://xbrl.sec.gov/currency/2023/currency-2023.xsd#currency_MXN"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_803ce861-ad90-4010-8681-f9883cfd2464" xlink:to="loc_currency_MXN_f3814cb3-f1bc-49f6-9875-1dd54974d4c9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_JPY_5e8afb03-f381-4ecb-b7d5-9b969540b5f7" xlink:href="https://xbrl.sec.gov/currency/2023/currency-2023.xsd#currency_JPY"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_803ce861-ad90-4010-8681-f9883cfd2464" xlink:to="loc_currency_JPY_5e8afb03-f381-4ecb-b7d5-9b969540b5f7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_HKD_59b08d72-ffb7-4af8-a0d8-93f6c0160d82" xlink:href="https://xbrl.sec.gov/currency/2023/currency-2023.xsd#currency_HKD"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_803ce861-ad90-4010-8681-f9883cfd2464" xlink:to="loc_currency_HKD_59b08d72-ffb7-4af8-a0d8-93f6c0160d82" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_VND_f19230f7-7cc7-4089-b6fe-5c0c5a761043" xlink:href="https://xbrl.sec.gov/currency/2023/currency-2023.xsd#currency_VND"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_803ce861-ad90-4010-8681-f9883cfd2464" xlink:to="loc_currency_VND_f19230f7-7cc7-4089-b6fe-5c0c5a761043" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_CNY_f7810421-0bb3-4426-b320-606481fb769d" xlink:href="https://xbrl.sec.gov/currency/2023/currency-2023.xsd#currency_CNY"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_803ce861-ad90-4010-8681-f9883cfd2464" xlink:to="loc_currency_CNY_f7810421-0bb3-4426-b320-606481fb769d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_MYR_58e588ac-76e3-4051-90c3-14a73cb78970" xlink:href="https://xbrl.sec.gov/currency/2023/currency-2023.xsd#currency_MYR"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_803ce861-ad90-4010-8681-f9883cfd2464" xlink:to="loc_currency_MYR_58e588ac-76e3-4051-90c3-14a73cb78970" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_8942b526-4275-4455-b015-7fb1dc2c7c3b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_d4443c56-a6c8-4ba3-9939-44c1a43e73d2" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_8942b526-4275-4455-b015-7fb1dc2c7c3b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/SummaryofSignificantAccountingPoliciesAdditionalInformationDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#SummaryofSignificantAccountingPoliciesAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/SummaryofSignificantAccountingPoliciesAdditionalInformationDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_gct_AccountingPoliciesLineItems_40ded518-c420-4f35-a96c-c4d7572800f2" xlink:href="gct-20231231.xsd#gct_AccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_AccountingPoliciesTable_f971b502-97c7-4277-b310-a259de48b6a1" xlink:href="gct-20231231.xsd#gct_AccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_gct_AccountingPoliciesLineItems_40ded518-c420-4f35-a96c-c4d7572800f2" xlink:to="loc_gct_AccountingPoliciesTable_f971b502-97c7-4277-b310-a259de48b6a1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_2d318fa2-23d0-4404-9e43-1b797b2a97e2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_AccountingPoliciesTable_f971b502-97c7-4277-b310-a259de48b6a1" xlink:to="loc_us-gaap_AwardTypeAxis_2d318fa2-23d0-4404-9e43-1b797b2a97e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2d318fa2-23d0-4404-9e43-1b797b2a97e2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_2d318fa2-23d0-4404-9e43-1b797b2a97e2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_2d318fa2-23d0-4404-9e43-1b797b2a97e2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_dd4120f7-04c1-436d-a322-c62a117b353a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_2d318fa2-23d0-4404-9e43-1b797b2a97e2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_dd4120f7-04c1-436d-a322-c62a117b353a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_98cbad83-0166-49b7-b298-ce6751bdfdb7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_dd4120f7-04c1-436d-a322-c62a117b353a" xlink:to="loc_us-gaap_EmployeeStockOptionMember_98cbad83-0166-49b7-b298-ce6751bdfdb7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_01e84415-f7f9-47d4-a3e3-d671d467d04c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_dd4120f7-04c1-436d-a322-c62a117b353a" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_01e84415-f7f9-47d4-a3e3-d671d467d04c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_5b3835eb-3da6-4281-8f3d-db8dd87aef90" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_AccountingPoliciesTable_f971b502-97c7-4277-b310-a259de48b6a1" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_5b3835eb-3da6-4281-8f3d-db8dd87aef90" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_5b3835eb-3da6-4281-8f3d-db8dd87aef90_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_5b3835eb-3da6-4281-8f3d-db8dd87aef90" xlink:to="loc_us-gaap_EquityComponentDomain_5b3835eb-3da6-4281-8f3d-db8dd87aef90_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_65439bf3-6fe0-4598-b570-e3aac9446542" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_5b3835eb-3da6-4281-8f3d-db8dd87aef90" xlink:to="loc_us-gaap_EquityComponentDomain_65439bf3-6fe0-4598-b570-e3aac9446542" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_5389ee39-9b8a-4e7b-a3e9-c23b566f0538" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_65439bf3-6fe0-4598-b570-e3aac9446542" xlink:to="loc_us-gaap_CommonStockMember_5389ee39-9b8a-4e7b-a3e9-c23b566f0538" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_aa5686d5-20fa-4c9c-ab71-d8d601a80b0f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_AccountingPoliciesTable_f971b502-97c7-4277-b310-a259de48b6a1" xlink:to="loc_us-gaap_StatementClassOfStockAxis_aa5686d5-20fa-4c9c-ab71-d8d601a80b0f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_aa5686d5-20fa-4c9c-ab71-d8d601a80b0f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_aa5686d5-20fa-4c9c-ab71-d8d601a80b0f" xlink:to="loc_us-gaap_ClassOfStockDomain_aa5686d5-20fa-4c9c-ab71-d8d601a80b0f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_8359be41-a2f7-4e6c-9d42-93d6a0367eed" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_aa5686d5-20fa-4c9c-ab71-d8d601a80b0f" xlink:to="loc_us-gaap_ClassOfStockDomain_8359be41-a2f7-4e6c-9d42-93d6a0367eed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableConvertiblePreferredStockMember_d2365791-0542-495d-ac7a-415449adc7d7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RedeemableConvertiblePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_8359be41-a2f7-4e6c-9d42-93d6a0367eed" xlink:to="loc_us-gaap_RedeemableConvertiblePreferredStockMember_d2365791-0542-495d-ac7a-415449adc7d7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_49b9519b-626d-43aa-8a2e-4b8dd7105cfa" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_AccountingPoliciesTable_f971b502-97c7-4277-b310-a259de48b6a1" xlink:to="loc_us-gaap_PlanNameAxis_49b9519b-626d-43aa-8a2e-4b8dd7105cfa" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_49b9519b-626d-43aa-8a2e-4b8dd7105cfa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_49b9519b-626d-43aa-8a2e-4b8dd7105cfa" xlink:to="loc_us-gaap_PlanNameDomain_49b9519b-626d-43aa-8a2e-4b8dd7105cfa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_c79d7b10-7278-49d0-8ce8-39e145a0ca48" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_49b9519b-626d-43aa-8a2e-4b8dd7105cfa" xlink:to="loc_us-gaap_PlanNameDomain_c79d7b10-7278-49d0-8ce8-39e145a0ca48" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_TwoThousandAndEightShareIncentivePlanMember_349e0e45-c044-44c3-b5ce-ae751f63e837" xlink:href="gct-20231231.xsd#gct_TwoThousandAndEightShareIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_c79d7b10-7278-49d0-8ce8-39e145a0ca48" xlink:to="loc_gct_TwoThousandAndEightShareIncentivePlanMember_349e0e45-c044-44c3-b5ce-ae751f63e837" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_TwoThousandAndSeventeenShareIncentivePlanMember_9968540c-4da0-475c-bbd6-935ca3b50409" xlink:href="gct-20231231.xsd#gct_TwoThousandAndSeventeenShareIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_c79d7b10-7278-49d0-8ce8-39e145a0ca48" xlink:to="loc_gct_TwoThousandAndSeventeenShareIncentivePlanMember_9968540c-4da0-475c-bbd6-935ca3b50409" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_b2f264e6-1cb1-4f5e-b748-702a74b1996d" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_AccountingPoliciesTable_f971b502-97c7-4277-b310-a259de48b6a1" xlink:to="loc_srt_StatementGeographicalAxis_b2f264e6-1cb1-4f5e-b748-702a74b1996d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_b2f264e6-1cb1-4f5e-b748-702a74b1996d_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_b2f264e6-1cb1-4f5e-b748-702a74b1996d" xlink:to="loc_srt_SegmentGeographicalDomain_b2f264e6-1cb1-4f5e-b748-702a74b1996d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_f64cb882-f846-44b5-84e8-795161ad95f6" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_b2f264e6-1cb1-4f5e-b748-702a74b1996d" xlink:to="loc_srt_SegmentGeographicalDomain_f64cb882-f846-44b5-84e8-795161ad95f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_917d370c-e58a-4fbb-8e86-33b7f5e06a23" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_f64cb882-f846-44b5-84e8-795161ad95f6" xlink:to="loc_country_US_917d370c-e58a-4fbb-8e86-33b7f5e06a23" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CurrencyAxis_bc5bd2b0-454f-4bc4-aa8f-7b2d5216e5b0" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CurrencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_AccountingPoliciesTable_f971b502-97c7-4277-b310-a259de48b6a1" xlink:to="loc_srt_CurrencyAxis_bc5bd2b0-454f-4bc4-aa8f-7b2d5216e5b0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_AllCurrenciesDomain_bc5bd2b0-454f-4bc4-aa8f-7b2d5216e5b0_default" xlink:href="https://xbrl.sec.gov/currency/2023/currency-2023.xsd#currency_AllCurrenciesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CurrencyAxis_bc5bd2b0-454f-4bc4-aa8f-7b2d5216e5b0" xlink:to="loc_currency_AllCurrenciesDomain_bc5bd2b0-454f-4bc4-aa8f-7b2d5216e5b0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_AllCurrenciesDomain_91d7c3fc-7f19-4ede-8274-3ef5d1c47b06" xlink:href="https://xbrl.sec.gov/currency/2023/currency-2023.xsd#currency_AllCurrenciesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CurrencyAxis_bc5bd2b0-454f-4bc4-aa8f-7b2d5216e5b0" xlink:to="loc_currency_AllCurrenciesDomain_91d7c3fc-7f19-4ede-8274-3ef5d1c47b06" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_USD_2adfe151-a646-4495-a2bb-9caffceda23f" xlink:href="https://xbrl.sec.gov/currency/2023/currency-2023.xsd#currency_USD"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_91d7c3fc-7f19-4ede-8274-3ef5d1c47b06" xlink:to="loc_currency_USD_2adfe151-a646-4495-a2bb-9caffceda23f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesLoansAndFinancingReceivablesByLegalEntityOfCounterpartyTypeAxis_99d3f356-361a-4ef6-b256-63068dc3372d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccountsNotesLoansAndFinancingReceivablesByLegalEntityOfCounterpartyTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_AccountingPoliciesTable_f971b502-97c7-4277-b310-a259de48b6a1" xlink:to="loc_us-gaap_AccountsNotesLoansAndFinancingReceivablesByLegalEntityOfCounterpartyTypeAxis_99d3f356-361a-4ef6-b256-63068dc3372d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LegalEntityTypeOfCounterpartyDomain_99d3f356-361a-4ef6-b256-63068dc3372d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LegalEntityTypeOfCounterpartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AccountsNotesLoansAndFinancingReceivablesByLegalEntityOfCounterpartyTypeAxis_99d3f356-361a-4ef6-b256-63068dc3372d" xlink:to="loc_us-gaap_LegalEntityTypeOfCounterpartyDomain_99d3f356-361a-4ef6-b256-63068dc3372d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LegalEntityTypeOfCounterpartyDomain_d046ce8f-253a-4210-8b8b-e800787c1e6f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LegalEntityTypeOfCounterpartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AccountsNotesLoansAndFinancingReceivablesByLegalEntityOfCounterpartyTypeAxis_99d3f356-361a-4ef6-b256-63068dc3372d" xlink:to="loc_us-gaap_LegalEntityTypeOfCounterpartyDomain_d046ce8f-253a-4210-8b8b-e800787c1e6f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GovernmentMember_6e03aca3-5791-4d39-b831-68da1654e9f3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LegalEntityTypeOfCounterpartyDomain_d046ce8f-253a-4210-8b8b-e800787c1e6f" xlink:to="loc_us-gaap_GovernmentMember_6e03aca3-5791-4d39-b831-68da1654e9f3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_9ff42db3-3ecf-4d90-ad3b-53cb14896eb2" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_AccountingPoliciesTable_f971b502-97c7-4277-b310-a259de48b6a1" xlink:to="loc_srt_MajorCustomersAxis_9ff42db3-3ecf-4d90-ad3b-53cb14896eb2" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_9ff42db3-3ecf-4d90-ad3b-53cb14896eb2_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_9ff42db3-3ecf-4d90-ad3b-53cb14896eb2" xlink:to="loc_srt_NameOfMajorCustomerDomain_9ff42db3-3ecf-4d90-ad3b-53cb14896eb2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_a639ece9-3618-49d0-82d8-3a63f82d4803" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_9ff42db3-3ecf-4d90-ad3b-53cb14896eb2" xlink:to="loc_srt_NameOfMajorCustomerDomain_a639ece9-3618-49d0-82d8-3a63f82d4803" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_NoCustomerMember_e0e8eb3b-0d8e-4d17-b3cc-1f64d4b2c772" xlink:href="gct-20231231.xsd#gct_NoCustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_a639ece9-3618-49d0-82d8-3a63f82d4803" xlink:to="loc_gct_NoCustomerMember_e0e8eb3b-0d8e-4d17-b3cc-1f64d4b2c772" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis_d48d9433-7a90-4473-9987-383ed6f3a85a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_AccountingPoliciesTable_f971b502-97c7-4277-b310-a259de48b6a1" xlink:to="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis_d48d9433-7a90-4473-9987-383ed6f3a85a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_d48d9433-7a90-4473-9987-383ed6f3a85a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis_d48d9433-7a90-4473-9987-383ed6f3a85a" xlink:to="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_d48d9433-7a90-4473-9987-383ed6f3a85a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_c63b7a8e-a802-41b1-aced-d35e1da7de65" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis_d48d9433-7a90-4473-9987-383ed6f3a85a" xlink:to="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_c63b7a8e-a802-41b1-aced-d35e1da7de65" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_OneSupplierMember_debe864f-3537-4cda-8a6a-3480cc349457" xlink:href="gct-20231231.xsd#gct_OneSupplierMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_c63b7a8e-a802-41b1-aced-d35e1da7de65" xlink:to="loc_gct_OneSupplierMember_debe864f-3537-4cda-8a6a-3480cc349457" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_NoSupplierMember_ef3a3516-3054-42a8-b39d-dd2c7880ed70" xlink:href="gct-20231231.xsd#gct_NoSupplierMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_c63b7a8e-a802-41b1-aced-d35e1da7de65" xlink:to="loc_gct_NoSupplierMember_ef3a3516-3054-42a8-b39d-dd2c7880ed70" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_793d764a-f361-45bf-b3a2-d56c5bf4a672" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_AccountingPoliciesTable_f971b502-97c7-4277-b310-a259de48b6a1" xlink:to="loc_srt_RangeAxis_793d764a-f361-45bf-b3a2-d56c5bf4a672" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_793d764a-f361-45bf-b3a2-d56c5bf4a672_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_793d764a-f361-45bf-b3a2-d56c5bf4a672" xlink:to="loc_srt_RangeMember_793d764a-f361-45bf-b3a2-d56c5bf4a672_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_f2fcf517-49e3-4925-9f80-9c8f01783eeb" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_793d764a-f361-45bf-b3a2-d56c5bf4a672" xlink:to="loc_srt_RangeMember_f2fcf517-49e3-4925-9f80-9c8f01783eeb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_cb6799fc-a528-492c-8d1b-6e24ee1af131" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_f2fcf517-49e3-4925-9f80-9c8f01783eeb" xlink:to="loc_srt_MinimumMember_cb6799fc-a528-492c-8d1b-6e24ee1af131" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_f32666a6-d4df-4dae-8c6b-8417a58fcc6d" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_f2fcf517-49e3-4925-9f80-9c8f01783eeb" xlink:to="loc_srt_MaximumMember_f32666a6-d4df-4dae-8c6b-8417a58fcc6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_14e0f396-4a89-4444-b08e-764610d7939d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_AccountingPoliciesTable_f971b502-97c7-4277-b310-a259de48b6a1" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_14e0f396-4a89-4444-b08e-764610d7939d" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_14e0f396-4a89-4444-b08e-764610d7939d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_14e0f396-4a89-4444-b08e-764610d7939d" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_14e0f396-4a89-4444-b08e-764610d7939d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_19396e9c-8c3a-4fea-b32c-f385d71d7569" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_14e0f396-4a89-4444-b08e-764610d7939d" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_19396e9c-8c3a-4fea-b32c-f385d71d7569" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_0a121e76-6072-4498-8918-f5f47bcef32b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_19396e9c-8c3a-4fea-b32c-f385d71d7569" xlink:to="loc_us-gaap_SalesRevenueNetMember_0a121e76-6072-4498-8918-f5f47bcef32b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PurchasesMember_d8b55945-5093-4c14-8c60-7d165b60b15c" xlink:href="gct-20231231.xsd#gct_PurchasesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_19396e9c-8c3a-4fea-b32c-f385d71d7569" xlink:to="loc_gct_PurchasesMember_d8b55945-5093-4c14-8c60-7d165b60b15c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_246e5ff4-c59a-4402-ae6f-f8ab9143de79" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_AccountingPoliciesTable_f971b502-97c7-4277-b310-a259de48b6a1" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_246e5ff4-c59a-4402-ae6f-f8ab9143de79" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_246e5ff4-c59a-4402-ae6f-f8ab9143de79_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_246e5ff4-c59a-4402-ae6f-f8ab9143de79" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_246e5ff4-c59a-4402-ae6f-f8ab9143de79_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_d376e71c-8f94-4719-8f96-4024ddf27016" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_246e5ff4-c59a-4402-ae6f-f8ab9143de79" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_d376e71c-8f94-4719-8f96-4024ddf27016" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_2be80182-7385-489a-aa1b-a33dba1e7cbe" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_d376e71c-8f94-4719-8f96-4024ddf27016" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_2be80182-7385-489a-aa1b-a33dba1e7cbe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplierConcentrationRiskMember_d1631c50-18f6-4fc0-ae00-dd817fdece78" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SupplierConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_d376e71c-8f94-4719-8f96-4024ddf27016" xlink:to="loc_us-gaap_SupplierConcentrationRiskMember_d1631c50-18f6-4fc0-ae00-dd817fdece78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_7eac403e-d1e1-40d9-b7d1-e7664180e24f" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_AccountingPoliciesTable_f971b502-97c7-4277-b310-a259de48b6a1" xlink:to="loc_srt_CounterpartyNameAxis_7eac403e-d1e1-40d9-b7d1-e7664180e24f" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_7eac403e-d1e1-40d9-b7d1-e7664180e24f_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_7eac403e-d1e1-40d9-b7d1-e7664180e24f" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_7eac403e-d1e1-40d9-b7d1-e7664180e24f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_aaaf5d47-6d38-4b83-902b-1204a00fb2a7" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_7eac403e-d1e1-40d9-b7d1-e7664180e24f" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_aaaf5d47-6d38-4b83-902b-1204a00fb2a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PRCSubsidiariesAndVIEsMember_f684a964-3975-4ceb-a7ae-064fdf18bdca" xlink:href="gct-20231231.xsd#gct_PRCSubsidiariesAndVIEsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_aaaf5d47-6d38-4b83-902b-1204a00fb2a7" xlink:to="loc_gct_PRCSubsidiariesAndVIEsMember_f684a964-3975-4ceb-a7ae-064fdf18bdca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityNoteStockSplitConversionRatio1_00f99d68-ac27-4c96-80b5-51b80f46d94b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquityNoteStockSplitConversionRatio1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_AccountingPoliciesLineItems_40ded518-c420-4f35-a96c-c4d7572800f2" xlink:to="loc_us-gaap_StockholdersEquityNoteStockSplitConversionRatio1_00f99d68-ac27-4c96-80b5-51b80f46d94b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue_fd59a490-8cab-455c-a884-cebea68557a7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_AccountingPoliciesLineItems_40ded518-c420-4f35-a96c-c4d7572800f2" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue_fd59a490-8cab-455c-a884-cebea68557a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedComputerSoftwareGross_e2fa61ea-5137-45e0-abbc-be1689d1fc06" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CapitalizedComputerSoftwareGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_AccountingPoliciesLineItems_40ded518-c420-4f35-a96c-c4d7572800f2" xlink:to="loc_us-gaap_CapitalizedComputerSoftwareGross_e2fa61ea-5137-45e0-abbc-be1689d1fc06" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_c647ad9f-13dd-481d-8d6e-3c70d26853d8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_AccountingPoliciesLineItems_40ded518-c420-4f35-a96c-c4d7572800f2" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_c647ad9f-13dd-481d-8d6e-3c70d26853d8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_ae7ad890-af48-4e63-bebf-e9d8c588960b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ImpairmentOfLongLivedAssetsHeldForUse"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_AccountingPoliciesLineItems_40ded518-c420-4f35-a96c-c4d7572800f2" xlink:to="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_ae7ad890-af48-4e63-bebf-e9d8c588960b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_NumberOfBusinessLines_e2462f80-e305-4e70-8062-01b56f90b8d4" xlink:href="gct-20231231.xsd#gct_NumberOfBusinessLines"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_AccountingPoliciesLineItems_40ded518-c420-4f35-a96c-c4d7572800f2" xlink:to="loc_gct_NumberOfBusinessLines_e2462f80-e305-4e70-8062-01b56f90b8d4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdvertisingExpense_93700904-1869-43bb-8bcb-ca8217c69c7d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdvertisingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_AccountingPoliciesLineItems_40ded518-c420-4f35-a96c-c4d7572800f2" xlink:to="loc_us-gaap_AdvertisingExpense_93700904-1869-43bb-8bcb-ca8217c69c7d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrantsReceivable_c23fdb32-daaa-4dcc-93e2-3fff1d64be0b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GrantsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_AccountingPoliciesLineItems_40ded518-c420-4f35-a96c-c4d7572800f2" xlink:to="loc_us-gaap_GrantsReceivable_c23fdb32-daaa-4dcc-93e2-3fff1d64be0b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent_95546a7f-b140-47b9-be4b-08203b3c85e7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_AccountingPoliciesLineItems_40ded518-c420-4f35-a96c-c4d7572800f2" xlink:to="loc_us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent_95546a7f-b140-47b9-be4b-08203b3c85e7" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedContributionPlanCostRecognized_98fc2fbc-d69e-4ee1-8893-c2895847b57d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DefinedContributionPlanCostRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_AccountingPoliciesLineItems_40ded518-c420-4f35-a96c-c4d7572800f2" xlink:to="loc_us-gaap_DefinedContributionPlanCostRecognized_98fc2fbc-d69e-4ee1-8893-c2895847b57d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ConcentrationRiskPercentage_797fb37a-0f0f-4acc-ab06-6a0b432239f7" xlink:href="gct-20231231.xsd#gct_ConcentrationRiskPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_AccountingPoliciesLineItems_40ded518-c420-4f35-a96c-c4d7572800f2" xlink:to="loc_gct_ConcentrationRiskPercentage_797fb37a-0f0f-4acc-ab06-6a0b432239f7" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_89b2fa3a-8a5a-4d5d-b638-a2fef2bc243b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_AccountingPoliciesLineItems_40ded518-c420-4f35-a96c-c4d7572800f2" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_89b2fa3a-8a5a-4d5d-b638-a2fef2bc243b" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyTransactionGainLossRealized_95901214-e557-474e-ae32-421690b1d1d9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ForeignCurrencyTransactionGainLossRealized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_AccountingPoliciesLineItems_40ded518-c420-4f35-a96c-c4d7572800f2" xlink:to="loc_us-gaap_ForeignCurrencyTransactionGainLossRealized_95901214-e557-474e-ae32-421690b1d1d9" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfOperatingSegments_7520259b-2ae4-421b-bc6c-8ce3c4d9ef6e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NumberOfOperatingSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_AccountingPoliciesLineItems_40ded518-c420-4f35-a96c-c4d7572800f2" xlink:to="loc_us-gaap_NumberOfOperatingSegments_7520259b-2ae4-421b-bc6c-8ce3c4d9ef6e" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PercentageOfAfterTaxProfitsToBeAppropriatedToStatutoryFund_cb97839a-7933-4ad7-9941-ff3423ec9437" xlink:href="gct-20231231.xsd#gct_PercentageOfAfterTaxProfitsToBeAppropriatedToStatutoryFund"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_AccountingPoliciesLineItems_40ded518-c420-4f35-a96c-c4d7572800f2" xlink:to="loc_gct_PercentageOfAfterTaxProfitsToBeAppropriatedToStatutoryFund_cb97839a-7933-4ad7-9941-ff3423ec9437" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_StatutorySurplusFundRequiredAsAPercentageOfRegisteredCapital_7f2911f9-bb76-46d7-9b06-301223866861" xlink:href="gct-20231231.xsd#gct_StatutorySurplusFundRequiredAsAPercentageOfRegisteredCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_AccountingPoliciesLineItems_40ded518-c420-4f35-a96c-c4d7572800f2" xlink:to="loc_gct_StatutorySurplusFundRequiredAsAPercentageOfRegisteredCapital_7f2911f9-bb76-46d7-9b06-301223866861" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAppropriated_e2b668c4-8b4a-4f17-a06a-fa90513f5b13" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RetainedEarningsAppropriated"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_AccountingPoliciesLineItems_40ded518-c420-4f35-a96c-c4d7572800f2" xlink:to="loc_us-gaap_RetainedEarningsAppropriated_e2b668c4-8b4a-4f17-a06a-fa90513f5b13" xlink:type="arc" order="16"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/SummaryofSignificantAccountingPoliciesSummaryofDepreciationonPropertyAndEquipmentDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#SummaryofSignificantAccountingPoliciesSummaryofDepreciationonPropertyAndEquipmentDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/SummaryofSignificantAccountingPoliciesSummaryofDepreciationonPropertyAndEquipmentDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_86749fc1-eb2d-4ec9-ab51-c8059208b696" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_8109d375-718b-4168-80c3-f7981e6b0191" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_86749fc1-eb2d-4ec9-ab51-c8059208b696" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_8109d375-718b-4168-80c3-f7981e6b0191" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_41ff472b-c55b-4bc4-b39a-0619ac69073e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_8109d375-718b-4168-80c3-f7981e6b0191" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_41ff472b-c55b-4bc4-b39a-0619ac69073e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_41ff472b-c55b-4bc4-b39a-0619ac69073e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_41ff472b-c55b-4bc4-b39a-0619ac69073e" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_41ff472b-c55b-4bc4-b39a-0619ac69073e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_7ed94fc0-aa91-4455-bcd9-f15934f9756e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_41ff472b-c55b-4bc4-b39a-0619ac69073e" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_7ed94fc0-aa91-4455-bcd9-f15934f9756e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OfficeEquipmentMember_88635ffe-e2f5-4111-a2c9-ad3f485b75f1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OfficeEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_7ed94fc0-aa91-4455-bcd9-f15934f9756e" xlink:to="loc_us-gaap_OfficeEquipmentMember_88635ffe-e2f5-4111-a2c9-ad3f485b75f1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VehiclesMember_e1ab1639-6e99-4aac-85b9-28c4a797c6f0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_VehiclesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_7ed94fc0-aa91-4455-bcd9-f15934f9756e" xlink:to="loc_us-gaap_VehiclesMember_e1ab1639-6e99-4aac-85b9-28c4a797c6f0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_LogisticsAndWarehouseAndOtherHeavyEquipmentMember_8ac69d38-2e68-497d-8580-ddf2786a4203" xlink:href="gct-20231231.xsd#gct_LogisticsAndWarehouseAndOtherHeavyEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_7ed94fc0-aa91-4455-bcd9-f15934f9756e" xlink:to="loc_gct_LogisticsAndWarehouseAndOtherHeavyEquipmentMember_8ac69d38-2e68-497d-8580-ddf2786a4203" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_1d7e9bd4-1e71-49b4-81b1-97ec7326ee50" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_8109d375-718b-4168-80c3-f7981e6b0191" xlink:to="loc_srt_RangeAxis_1d7e9bd4-1e71-49b4-81b1-97ec7326ee50" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_1d7e9bd4-1e71-49b4-81b1-97ec7326ee50_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_1d7e9bd4-1e71-49b4-81b1-97ec7326ee50" xlink:to="loc_srt_RangeMember_1d7e9bd4-1e71-49b4-81b1-97ec7326ee50_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_00d84392-d8b1-4076-849b-7a5c591c370a" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_1d7e9bd4-1e71-49b4-81b1-97ec7326ee50" xlink:to="loc_srt_RangeMember_00d84392-d8b1-4076-849b-7a5c591c370a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_b35d4e1a-8dbd-40df-9a57-061252ea9b50" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_00d84392-d8b1-4076-849b-7a5c591c370a" xlink:to="loc_srt_MinimumMember_b35d4e1a-8dbd-40df-9a57-061252ea9b50" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_569bd0a2-0139-4e1d-9b0f-4c6408aeeb4b" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_00d84392-d8b1-4076-849b-7a5c591c370a" xlink:to="loc_srt_MaximumMember_569bd0a2-0139-4e1d-9b0f-4c6408aeeb4b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_5436307d-f741-41cd-8815-e5c1370defad" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_86749fc1-eb2d-4ec9-ab51-c8059208b696" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_5436307d-f741-41cd-8815-e5c1370defad" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/SummaryofSignificantAccountingPoliciesSummaryofAccountsReceivableBalanceDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#SummaryofSignificantAccountingPoliciesSummaryofAccountsReceivableBalanceDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/SummaryofSignificantAccountingPoliciesSummaryofAccountsReceivableBalanceDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_e5c34f43-442b-4819-b775-dee8f8397464" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_7bce8eb8-8b73-4ae4-8d17-b32a15c8b049" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_e5c34f43-442b-4819-b775-dee8f8397464" xlink:to="loc_us-gaap_StatementTable_7bce8eb8-8b73-4ae4-8d17-b32a15c8b049" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_c28a1bbe-7921-4752-8212-0a4945722ab6" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_7bce8eb8-8b73-4ae4-8d17-b32a15c8b049" xlink:to="loc_srt_MajorCustomersAxis_c28a1bbe-7921-4752-8212-0a4945722ab6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_c28a1bbe-7921-4752-8212-0a4945722ab6_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_c28a1bbe-7921-4752-8212-0a4945722ab6" xlink:to="loc_srt_NameOfMajorCustomerDomain_c28a1bbe-7921-4752-8212-0a4945722ab6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_ca16df77-59ce-4e8e-89e6-c4beb3046858" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_c28a1bbe-7921-4752-8212-0a4945722ab6" xlink:to="loc_srt_NameOfMajorCustomerDomain_ca16df77-59ce-4e8e-89e6-c4beb3046858" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ThreeCustomerMember_8d78b7aa-c3b0-4ddf-b36c-df639a8aaf88" xlink:href="gct-20231231.xsd#gct_ThreeCustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_ca16df77-59ce-4e8e-89e6-c4beb3046858" xlink:to="loc_gct_ThreeCustomerMember_8d78b7aa-c3b0-4ddf-b36c-df639a8aaf88" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_OneCustomerMember_a1e05725-efee-42e6-829a-bad25b4f5a83" xlink:href="gct-20231231.xsd#gct_OneCustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_ca16df77-59ce-4e8e-89e6-c4beb3046858" xlink:to="loc_gct_OneCustomerMember_a1e05725-efee-42e6-829a-bad25b4f5a83" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_CustomerAMember_a8fdb88e-5ccb-4683-b9dd-8619e67c14d4" xlink:href="gct-20231231.xsd#gct_CustomerAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_ca16df77-59ce-4e8e-89e6-c4beb3046858" xlink:to="loc_gct_CustomerAMember_a8fdb88e-5ccb-4683-b9dd-8619e67c14d4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_CustomerBMember_60a4efb4-c150-4998-8b52-7211f1b118fe" xlink:href="gct-20231231.xsd#gct_CustomerBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_ca16df77-59ce-4e8e-89e6-c4beb3046858" xlink:to="loc_gct_CustomerBMember_60a4efb4-c150-4998-8b52-7211f1b118fe" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_CustomerCMember_dc3e5a51-c30b-496a-a661-ef2f881a7d01" xlink:href="gct-20231231.xsd#gct_CustomerCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_ca16df77-59ce-4e8e-89e6-c4beb3046858" xlink:to="loc_gct_CustomerCMember_dc3e5a51-c30b-496a-a661-ef2f881a7d01" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_6218bd85-fa04-4b3c-a51f-76edfb5e10d0" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_7bce8eb8-8b73-4ae4-8d17-b32a15c8b049" xlink:to="loc_srt_RangeAxis_6218bd85-fa04-4b3c-a51f-76edfb5e10d0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_6218bd85-fa04-4b3c-a51f-76edfb5e10d0_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_6218bd85-fa04-4b3c-a51f-76edfb5e10d0" xlink:to="loc_srt_RangeMember_6218bd85-fa04-4b3c-a51f-76edfb5e10d0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_1d328768-3082-453d-b358-a36d7515530c" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_6218bd85-fa04-4b3c-a51f-76edfb5e10d0" xlink:to="loc_srt_RangeMember_1d328768-3082-453d-b358-a36d7515530c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_122b9c21-b256-4092-848e-c9c67ec0770d" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_1d328768-3082-453d-b358-a36d7515530c" xlink:to="loc_srt_MinimumMember_122b9c21-b256-4092-848e-c9c67ec0770d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_8347d784-0036-44e6-b016-a40a4396bea7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_7bce8eb8-8b73-4ae4-8d17-b32a15c8b049" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_8347d784-0036-44e6-b016-a40a4396bea7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_8347d784-0036-44e6-b016-a40a4396bea7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_8347d784-0036-44e6-b016-a40a4396bea7" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_8347d784-0036-44e6-b016-a40a4396bea7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_ee07d551-7907-4526-bbe6-59a6ae427747" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_8347d784-0036-44e6-b016-a40a4396bea7" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_ee07d551-7907-4526-bbe6-59a6ae427747" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableMember_6eed8224-6a7e-4038-b943-92bcc3059910" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_ee07d551-7907-4526-bbe6-59a6ae427747" xlink:to="loc_us-gaap_AccountsReceivableMember_6eed8224-6a7e-4038-b943-92bcc3059910" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_e90c7972-f6a1-48cd-95a0-fbce9298ad48" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_ee07d551-7907-4526-bbe6-59a6ae427747" xlink:to="loc_us-gaap_SalesRevenueNetMember_e90c7972-f6a1-48cd-95a0-fbce9298ad48" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_ec9a11dc-db84-4b31-9dd9-30f85863f523" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_7bce8eb8-8b73-4ae4-8d17-b32a15c8b049" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_ec9a11dc-db84-4b31-9dd9-30f85863f523" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_ec9a11dc-db84-4b31-9dd9-30f85863f523_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_ec9a11dc-db84-4b31-9dd9-30f85863f523" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_ec9a11dc-db84-4b31-9dd9-30f85863f523_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_add64cf2-a77d-4924-8ee8-686b8e01b24b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_ec9a11dc-db84-4b31-9dd9-30f85863f523" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_add64cf2-a77d-4924-8ee8-686b8e01b24b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_6d7c3799-65d0-4904-8624-c9662173e0b1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_add64cf2-a77d-4924-8ee8-686b8e01b24b" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_6d7c3799-65d0-4904-8624-c9662173e0b1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ConcentrationRiskPercentage_dcf1e3ac-a99e-4c49-84bd-2bd564cfd26f" xlink:href="gct-20231231.xsd#gct_ConcentrationRiskPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_e5c34f43-442b-4819-b775-dee8f8397464" xlink:to="loc_gct_ConcentrationRiskPercentage_dcf1e3ac-a99e-4c49-84bd-2bd564cfd26f" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/SummaryofSignificantAccountingPoliciesSummaryofLonglivedAssetsbySegmentDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#SummaryofSignificantAccountingPoliciesSummaryofLonglivedAssetsbySegmentDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/SummaryofSignificantAccountingPoliciesSummaryofLonglivedAssetsbySegmentDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_3c011da8-3e85-49af-b9f3-96a034ce0741" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_44554f69-2f98-43dc-af8a-d990cf480e2e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_3c011da8-3e85-49af-b9f3-96a034ce0741" xlink:to="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_44554f69-2f98-43dc-af8a-d990cf480e2e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_abbb4d97-3a19-4ad3-9772-2552a9bb66bb" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_44554f69-2f98-43dc-af8a-d990cf480e2e" xlink:to="loc_srt_StatementGeographicalAxis_abbb4d97-3a19-4ad3-9772-2552a9bb66bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_abbb4d97-3a19-4ad3-9772-2552a9bb66bb_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_abbb4d97-3a19-4ad3-9772-2552a9bb66bb" xlink:to="loc_srt_SegmentGeographicalDomain_abbb4d97-3a19-4ad3-9772-2552a9bb66bb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_e2acd6ff-7cd3-4d6b-afa4-9e2995516904" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_abbb4d97-3a19-4ad3-9772-2552a9bb66bb" xlink:to="loc_srt_SegmentGeographicalDomain_e2acd6ff-7cd3-4d6b-afa4-9e2995516904" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_71ee5852-e112-4fb6-939e-5367ae7d970e" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_e2acd6ff-7cd3-4d6b-afa4-9e2995516904" xlink:to="loc_country_US_71ee5852-e112-4fb6-939e-5367ae7d970e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_OthersMember_43954ce8-714c-4d63-8655-2b20bb69ed22" xlink:href="gct-20231231.xsd#gct_OthersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_e2acd6ff-7cd3-4d6b-afa4-9e2995516904" xlink:to="loc_gct_OthersMember_43954ce8-714c-4d63-8655-2b20bb69ed22" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncurrentAssets_5ce6cc57-2437-45a3-864a-705bb8a03949" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NoncurrentAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_3c011da8-3e85-49af-b9f3-96a034ce0741" xlink:to="loc_us-gaap_NoncurrentAssets_5ce6cc57-2437-45a3-864a-705bb8a03949" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/SummaryofSignificantAccountingPoliciesSummaryofGeographicinformationofRevenuebySegmentDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#SummaryofSignificantAccountingPoliciesSummaryofGeographicinformationofRevenuebySegmentDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/SummaryofSignificantAccountingPoliciesSummaryofGeographicinformationofRevenuebySegmentDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_705ed104-981e-41d2-ba17-22ebb6109953" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_f40648ec-3e03-47e1-afba-299ace254019" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_705ed104-981e-41d2-ba17-22ebb6109953" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_f40648ec-3e03-47e1-afba-299ace254019" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_6e698300-73b5-4c10-82e5-b237b2c59555" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_f40648ec-3e03-47e1-afba-299ace254019" xlink:to="loc_srt_ProductOrServiceAxis_6e698300-73b5-4c10-82e5-b237b2c59555" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_6e698300-73b5-4c10-82e5-b237b2c59555_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_6e698300-73b5-4c10-82e5-b237b2c59555" xlink:to="loc_srt_ProductsAndServicesDomain_6e698300-73b5-4c10-82e5-b237b2c59555_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_5b1dec3c-c4d8-4743-8eba-374a638c0432" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_6e698300-73b5-4c10-82e5-b237b2c59555" xlink:to="loc_srt_ProductsAndServicesDomain_5b1dec3c-c4d8-4743-8eba-374a638c0432" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServiceMember_e502adbd-9a03-4f99-b545-13eb0e32f999" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_5b1dec3c-c4d8-4743-8eba-374a638c0432" xlink:to="loc_us-gaap_ServiceMember_e502adbd-9a03-4f99-b545-13eb0e32f999" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PlatformCommissionMember_8d972dd2-2c50-49d3-ae17-037eefb0d68c" xlink:href="gct-20231231.xsd#gct_PlatformCommissionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_5b1dec3c-c4d8-4743-8eba-374a638c0432" xlink:to="loc_gct_PlatformCommissionMember_8d972dd2-2c50-49d3-ae17-037eefb0d68c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_OceanTransportationServiceMember_217a9521-d5fc-4afb-a707-defb9c24ec70" xlink:href="gct-20231231.xsd#gct_OceanTransportationServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_5b1dec3c-c4d8-4743-8eba-374a638c0432" xlink:to="loc_gct_OceanTransportationServiceMember_217a9521-d5fc-4afb-a707-defb9c24ec70" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_WarehousingServiceMember_fe9b0b4a-ad4a-422f-b924-e588dea35c48" xlink:href="gct-20231231.xsd#gct_WarehousingServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_5b1dec3c-c4d8-4743-8eba-374a638c0432" xlink:to="loc_gct_WarehousingServiceMember_fe9b0b4a-ad4a-422f-b924-e588dea35c48" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_LastmileDeliveryServiceMember_002023c3-5d10-4778-87c9-bc88d4a41743" xlink:href="gct-20231231.xsd#gct_LastmileDeliveryServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_5b1dec3c-c4d8-4743-8eba-374a638c0432" xlink:to="loc_gct_LastmileDeliveryServiceMember_002023c3-5d10-4778-87c9-bc88d4a41743" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PackagingServiceMember_d84b1f36-5ed6-43d3-a75f-376c25d0b427" xlink:href="gct-20231231.xsd#gct_PackagingServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_5b1dec3c-c4d8-4743-8eba-374a638c0432" xlink:to="loc_gct_PackagingServiceMember_d84b1f36-5ed6-43d3-a75f-376c25d0b427" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServiceOtherMember_36c80cd2-8922-4080-b3b5-a5aae214633d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ServiceOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_5b1dec3c-c4d8-4743-8eba-374a638c0432" xlink:to="loc_us-gaap_ServiceOtherMember_36c80cd2-8922-4080-b3b5-a5aae214633d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_3dc04311-34f6-4055-958c-c969ccb60450" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_5b1dec3c-c4d8-4743-8eba-374a638c0432" xlink:to="loc_us-gaap_ProductMember_3dc04311-34f6-4055-958c-c969ccb60450" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_c7b63e0e-6c26-4c9c-aa0d-4571c4188a2f" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_f40648ec-3e03-47e1-afba-299ace254019" xlink:to="loc_srt_StatementGeographicalAxis_c7b63e0e-6c26-4c9c-aa0d-4571c4188a2f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_c7b63e0e-6c26-4c9c-aa0d-4571c4188a2f_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_c7b63e0e-6c26-4c9c-aa0d-4571c4188a2f" xlink:to="loc_srt_SegmentGeographicalDomain_c7b63e0e-6c26-4c9c-aa0d-4571c4188a2f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_29646680-be12-4ef8-8c9a-9bf18b218537" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_c7b63e0e-6c26-4c9c-aa0d-4571c4188a2f" xlink:to="loc_srt_SegmentGeographicalDomain_29646680-be12-4ef8-8c9a-9bf18b218537" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_7f5b80b2-6f1a-4584-a484-17746b0db2bf" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_29646680-be12-4ef8-8c9a-9bf18b218537" xlink:to="loc_country_US_7f5b80b2-6f1a-4584-a484-17746b0db2bf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_JP_9494681a-bc6e-4837-a94b-0946c1a72b32" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_JP"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_29646680-be12-4ef8-8c9a-9bf18b218537" xlink:to="loc_country_JP_9494681a-bc6e-4837-a94b-0946c1a72b32" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_DE_f751e623-1756-4823-8fae-9e718ed4618a" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_DE"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_29646680-be12-4ef8-8c9a-9bf18b218537" xlink:to="loc_country_DE_f751e623-1756-4823-8fae-9e718ed4618a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_OthersMember_277594c0-3e0e-460f-8280-ad05b6741bd9" xlink:href="gct-20231231.xsd#gct_OthersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_29646680-be12-4ef8-8c9a-9bf18b218537" xlink:to="loc_gct_OthersMember_277594c0-3e0e-460f-8280-ad05b6741bd9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_HK_ee811646-a180-4a78-90df-b553d868cd61" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_HK"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_29646680-be12-4ef8-8c9a-9bf18b218537" xlink:to="loc_country_HK_ee811646-a180-4a78-90df-b553d868cd61" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_NoRegionMember_7fc3df15-ff41-4b40-8e2a-d26d851dfbf8" xlink:href="gct-20231231.xsd#gct_NoRegionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_29646680-be12-4ef8-8c9a-9bf18b218537" xlink:to="loc_gct_NoRegionMember_7fc3df15-ff41-4b40-8e2a-d26d851dfbf8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_fd55c29d-d2a8-4de6-b05f-3fda3fe027fa" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_f40648ec-3e03-47e1-afba-299ace254019" xlink:to="loc_srt_RangeAxis_fd55c29d-d2a8-4de6-b05f-3fda3fe027fa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_fd55c29d-d2a8-4de6-b05f-3fda3fe027fa_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_fd55c29d-d2a8-4de6-b05f-3fda3fe027fa" xlink:to="loc_srt_RangeMember_fd55c29d-d2a8-4de6-b05f-3fda3fe027fa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_94ec68c3-9e77-4dda-b751-31eb54feac1b" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_fd55c29d-d2a8-4de6-b05f-3fda3fe027fa" xlink:to="loc_srt_RangeMember_94ec68c3-9e77-4dda-b751-31eb54feac1b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_e47036af-2ca8-4012-942f-119dc0164615" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_94ec68c3-9e77-4dda-b751-31eb54feac1b" xlink:to="loc_srt_MinimumMember_e47036af-2ca8-4012-942f-119dc0164615" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_d1190b53-3acc-45db-a455-5a5adbc9b16c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_f40648ec-3e03-47e1-afba-299ace254019" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_d1190b53-3acc-45db-a455-5a5adbc9b16c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_d1190b53-3acc-45db-a455-5a5adbc9b16c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_d1190b53-3acc-45db-a455-5a5adbc9b16c" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_d1190b53-3acc-45db-a455-5a5adbc9b16c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_a29447db-42b3-4e6d-aaa4-8da76e2f549d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_d1190b53-3acc-45db-a455-5a5adbc9b16c" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_a29447db-42b3-4e6d-aaa4-8da76e2f549d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_d00dfede-fee5-4e3a-9f1b-d48855f22590" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_a29447db-42b3-4e6d-aaa4-8da76e2f549d" xlink:to="loc_us-gaap_SalesRevenueNetMember_d00dfede-fee5-4e3a-9f1b-d48855f22590" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_ce4b7083-2031-4fa6-882d-159ae0b51e61" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_705ed104-981e-41d2-ba17-22ebb6109953" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_ce4b7083-2031-4fa6-882d-159ae0b51e61" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_294187de-691c-44ba-9ecb-feabf42e910e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_705ed104-981e-41d2-ba17-22ebb6109953" xlink:to="loc_us-gaap_Revenues_294187de-691c-44ba-9ecb-feabf42e910e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ConcentrationRiskPercentage_d9db2900-d050-4737-b0ba-ba0c466712d4" xlink:href="gct-20231231.xsd#gct_ConcentrationRiskPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_705ed104-981e-41d2-ba17-22ebb6109953" xlink:to="loc_gct_ConcentrationRiskPercentage_d9db2900-d050-4737-b0ba-ba0c466712d4" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/BusinessCombinationsNarrativeDetails" xlink:type="simple" xlink:href="gct-20231231.xsd#BusinessCombinationsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://gig.com/role/BusinessCombinationsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_aa856670-8d70-4bed-b807-273f30f0419f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable_edfc43bd-88ab-47c2-b554-d56a96622e33" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_aa856670-8d70-4bed-b807-273f30f0419f" xlink:to="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable_edfc43bd-88ab-47c2-b554-d56a96622e33" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_5e4c3803-e046-4d0d-aaf0-69adad5c1dd9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable_edfc43bd-88ab-47c2-b554-d56a96622e33" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_5e4c3803-e046-4d0d-aaf0-69adad5c1dd9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_5e4c3803-e046-4d0d-aaf0-69adad5c1dd9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_5e4c3803-e046-4d0d-aaf0-69adad5c1dd9" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_5e4c3803-e046-4d0d-aaf0-69adad5c1dd9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3e86b455-5c29-4711-9790-f80cc7a5ce61" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_5e4c3803-e046-4d0d-aaf0-69adad5c1dd9" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3e86b455-5c29-4711-9790-f80cc7a5ce61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_NobleHouseHomeFurnishingsLLCMember_a0e9a789-6348-4782-9b90-65810dd9d94d" xlink:href="gct-20231231.xsd#gct_NobleHouseHomeFurnishingsLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3e86b455-5c29-4711-9790-f80cc7a5ce61" xlink:to="loc_gct_NobleHouseHomeFurnishingsLLCMember_a0e9a789-6348-4782-9b90-65810dd9d94d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_WondersignMember_972dca58-b83b-4c59-8aad-d7a747e62cd5" xlink:href="gct-20231231.xsd#gct_WondersignMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3e86b455-5c29-4711-9790-f80cc7a5ce61" xlink:to="loc_gct_WondersignMember_972dca58-b83b-4c59-8aad-d7a747e62cd5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_3ff03ceb-2a71-4a39-ae65-f6eb19960a91" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable_edfc43bd-88ab-47c2-b554-d56a96622e33" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_3ff03ceb-2a71-4a39-ae65-f6eb19960a91" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3ff03ceb-2a71-4a39-ae65-f6eb19960a91_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_3ff03ceb-2a71-4a39-ae65-f6eb19960a91" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3ff03ceb-2a71-4a39-ae65-f6eb19960a91_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_670c9bb6-dbb4-49c0-9edc-8d8f9ab689bb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_3ff03ceb-2a71-4a39-ae65-f6eb19960a91" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_670c9bb6-dbb4-49c0-9edc-8d8f9ab689bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_79b0184d-103f-4b3e-b1b7-69848bbc03b6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_670c9bb6-dbb4-49c0-9edc-8d8f9ab689bb" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_79b0184d-103f-4b3e-b1b7-69848bbc03b6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_02c37f68-7ec2-4993-92cc-203ba09b2e5e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_670c9bb6-dbb4-49c0-9edc-8d8f9ab689bb" xlink:to="loc_us-gaap_CustomerRelationshipsMember_02c37f68-7ec2-4993-92cc-203ba09b2e5e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_0af7438f-967b-4d6f-9d3e-692d0b89f015" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable_edfc43bd-88ab-47c2-b554-d56a96622e33" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_0af7438f-967b-4d6f-9d3e-692d0b89f015" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_0af7438f-967b-4d6f-9d3e-692d0b89f015_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_0af7438f-967b-4d6f-9d3e-692d0b89f015" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_0af7438f-967b-4d6f-9d3e-692d0b89f015_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_e8bd4e33-8a86-4894-bfd2-d800f2518e40" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_0af7438f-967b-4d6f-9d3e-692d0b89f015" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_e8bd4e33-8a86-4894-bfd2-d800f2518e40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_019c0624-8d2f-41f0-a211-d20d810492f4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_e8bd4e33-8a86-4894-bfd2-d800f2518e40" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_019c0624-8d2f-41f0-a211-d20d810492f4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_f7172486-7f4d-4db4-ab28-2f05d955cd50" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_aa856670-8d70-4bed-b807-273f30f0419f" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_f7172486-7f4d-4db4-ab28-2f05d955cd50" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_dfdd9f28-a199-4896-abc1-9ce7ff668cdb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_aa856670-8d70-4bed-b807-273f30f0419f" xlink:to="loc_us-gaap_Goodwill_dfdd9f28-a199-4896-abc1-9ce7ff668cdb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinitelivedIntangibleAssetsAcquired1_6a0cff0f-64e8-4100-a45b-5b690d7bb853" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FinitelivedIntangibleAssetsAcquired1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_aa856670-8d70-4bed-b807-273f30f0419f" xlink:to="loc_us-gaap_FinitelivedIntangibleAssetsAcquired1_6a0cff0f-64e8-4100-a45b-5b690d7bb853" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_41a69c10-9fe3-4a6d-b054-eb7d47fe8929" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_aa856670-8d70-4bed-b807-273f30f0419f" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_41a69c10-9fe3-4a6d-b054-eb7d47fe8929" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_15cf39e0-b8ae-44c2-8a80-0a6679382674" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationAcquisitionRelatedCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_aa856670-8d70-4bed-b807-273f30f0419f" xlink:to="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_15cf39e0-b8ae-44c2-8a80-0a6679382674" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/BusinessCombinationsNobleHouseDetails" xlink:type="simple" xlink:href="gct-20231231.xsd#BusinessCombinationsNobleHouseDetails"/>
  <link:definitionLink xlink:role="http://gig.com/role/BusinessCombinationsNobleHouseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_37b9f03e-cdf1-476b-8809-f8877dfb9393" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable_6e08b5ff-2f77-4b47-8026-b31cf81e0c5f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_37b9f03e-cdf1-476b-8809-f8877dfb9393" xlink:to="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable_6e08b5ff-2f77-4b47-8026-b31cf81e0c5f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_44c00272-933c-4ee8-bfcf-47b5ccf39048" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable_6e08b5ff-2f77-4b47-8026-b31cf81e0c5f" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_44c00272-933c-4ee8-bfcf-47b5ccf39048" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_44c00272-933c-4ee8-bfcf-47b5ccf39048_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_44c00272-933c-4ee8-bfcf-47b5ccf39048" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_44c00272-933c-4ee8-bfcf-47b5ccf39048_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_af294ee5-ffeb-4800-bb98-60e91ef0e734" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_44c00272-933c-4ee8-bfcf-47b5ccf39048" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_af294ee5-ffeb-4800-bb98-60e91ef0e734" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_NobleHouseHomeFurnishingsLLCMember_96ddb02b-5896-4940-8232-2999a633da4e" xlink:href="gct-20231231.xsd#gct_NobleHouseHomeFurnishingsLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_af294ee5-ffeb-4800-bb98-60e91ef0e734" xlink:to="loc_gct_NobleHouseHomeFurnishingsLLCMember_96ddb02b-5896-4940-8232-2999a633da4e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_ed1e06fb-b42d-4701-a572-3678074cccd6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_37b9f03e-cdf1-476b-8809-f8877dfb9393" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_ed1e06fb-b42d-4701-a572-3678074cccd6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_d34aa337-980c-4643-a25e-a769d182ea37" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_37b9f03e-cdf1-476b-8809-f8877dfb9393" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_d34aa337-980c-4643-a25e-a769d182ea37" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_7f95d225-e9d7-4adb-9e01-191e13e8920c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_37b9f03e-cdf1-476b-8809-f8877dfb9393" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_7f95d225-e9d7-4adb-9e01-191e13e8920c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_38c2ce5b-e367-4541-b75c-be7d8e58533c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_37b9f03e-cdf1-476b-8809-f8877dfb9393" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_38c2ce5b-e367-4541-b75c-be7d8e58533c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOperatingLeaseRightOfUseAssets_fd10c3cf-cc6c-4d1e-b15a-3ca3c758e1c7" xlink:href="gct-20231231.xsd#gct_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOperatingLeaseRightOfUseAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_37b9f03e-cdf1-476b-8809-f8877dfb9393" xlink:to="loc_gct_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOperatingLeaseRightOfUseAssets_fd10c3cf-cc6c-4d1e-b15a-3ca3c758e1c7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_65afe3c7-d532-42fc-a11e-5101e44adb2d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_37b9f03e-cdf1-476b-8809-f8877dfb9393" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_65afe3c7-d532-42fc-a11e-5101e44adb2d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_b97a14f3-6968-4372-bf37-6e486b422e30" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_37b9f03e-cdf1-476b-8809-f8877dfb9393" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_b97a14f3-6968-4372-bf37-6e486b422e30" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssets_3fcf16e3-b98a-4533-be67-d67a24531dd3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_37b9f03e-cdf1-476b-8809-f8877dfb9393" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssets_3fcf16e3-b98a-4533-be67-d67a24531dd3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_09a57fe7-7b4a-4750-a735-67f71ec3ae2c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_37b9f03e-cdf1-476b-8809-f8877dfb9393" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_09a57fe7-7b4a-4750-a735-67f71ec3ae2c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_acc5fb58-a92b-408e-91e9-b3da86b30dba" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_37b9f03e-cdf1-476b-8809-f8877dfb9393" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_acc5fb58-a92b-408e-91e9-b3da86b30dba" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesDeferredRevenue_1eff7da2-c300-4b6f-b097-6eae79515561" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesDeferredRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_37b9f03e-cdf1-476b-8809-f8877dfb9393" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesDeferredRevenue_1eff7da2-c300-4b6f-b097-6eae79515561" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesCurrentOperatingLeaseLiabilities_12b908a2-02ac-4010-9d58-7d3b2f8afde8" xlink:href="gct-20231231.xsd#gct_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesCurrentOperatingLeaseLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_37b9f03e-cdf1-476b-8809-f8877dfb9393" xlink:to="loc_gct_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesCurrentOperatingLeaseLiabilities_12b908a2-02ac-4010-9d58-7d3b2f8afde8" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities_4bc17737-ab74-42cc-bc3b-102d536aa687" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_37b9f03e-cdf1-476b-8809-f8877dfb9393" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities_4bc17737-ab74-42cc-bc3b-102d536aa687" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOperatingLeaseLiabilitiesNonCurrent_9d626e07-c5c4-4fe6-bb62-1790145153f6" xlink:href="gct-20231231.xsd#gct_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOperatingLeaseLiabilitiesNonCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_37b9f03e-cdf1-476b-8809-f8877dfb9393" xlink:to="loc_gct_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOperatingLeaseLiabilitiesNonCurrent_9d626e07-c5c4-4fe6-bb62-1790145153f6" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesFinanceLeaseObligationsNonCurrent_41769d27-63cf-4750-9011-4dcaeeaa38dc" xlink:href="gct-20231231.xsd#gct_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesFinanceLeaseObligationsNonCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_37b9f03e-cdf1-476b-8809-f8877dfb9393" xlink:to="loc_gct_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesFinanceLeaseObligationsNonCurrent_41769d27-63cf-4750-9011-4dcaeeaa38dc" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet_0dedf8a2-47ac-4f46-8a64-975650c05e27" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_37b9f03e-cdf1-476b-8809-f8877dfb9393" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet_0dedf8a2-47ac-4f46-8a64-975650c05e27" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_cb96d55e-a02c-4292-9533-e49aecc3094b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_37b9f03e-cdf1-476b-8809-f8877dfb9393" xlink:to="loc_us-gaap_Goodwill_cb96d55e-a02c-4292-9533-e49aecc3094b" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_b633b5c2-86a2-4f2f-a3f6-d31a39e3011e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_37b9f03e-cdf1-476b-8809-f8877dfb9393" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_b633b5c2-86a2-4f2f-a3f6-d31a39e3011e" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual_22443406-d30a-4f68-8087-3e630409f77e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_37b9f03e-cdf1-476b-8809-f8877dfb9393" xlink:to="loc_us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual_22443406-d30a-4f68-8087-3e630409f77e" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual_ef9ccaaf-0643-481f-a0e9-4bf00eff9002" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_37b9f03e-cdf1-476b-8809-f8877dfb9393" xlink:to="loc_us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual_ef9ccaaf-0643-481f-a0e9-4bf00eff9002" xlink:type="arc" order="19"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/BusinessCombinationsProFormaInformationDetails" xlink:type="simple" xlink:href="gct-20231231.xsd#BusinessCombinationsProFormaInformationDetails"/>
  <link:definitionLink xlink:role="http://gig.com/role/BusinessCombinationsProFormaInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_a559be9e-a7d1-4307-a03a-2ccc51957045" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable_94ab1114-e5d0-4f75-90cf-1fbb0427fe68" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_a559be9e-a7d1-4307-a03a-2ccc51957045" xlink:to="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable_94ab1114-e5d0-4f75-90cf-1fbb0427fe68" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_29d58884-2dac-4999-9a6a-de89cd59c840" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable_94ab1114-e5d0-4f75-90cf-1fbb0427fe68" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_29d58884-2dac-4999-9a6a-de89cd59c840" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_29d58884-2dac-4999-9a6a-de89cd59c840_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_29d58884-2dac-4999-9a6a-de89cd59c840" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_29d58884-2dac-4999-9a6a-de89cd59c840_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_36733ed0-1fc0-440d-80d2-9715d7bbd811" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_29d58884-2dac-4999-9a6a-de89cd59c840" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_36733ed0-1fc0-440d-80d2-9715d7bbd811" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_NobleHouseHomeFurnishingsLLCMember_9c54f4cb-4b62-4a7f-ade9-e7a8b430d94d" xlink:href="gct-20231231.xsd#gct_NobleHouseHomeFurnishingsLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_36733ed0-1fc0-440d-80d2-9715d7bbd811" xlink:to="loc_gct_NobleHouseHomeFurnishingsLLCMember_9c54f4cb-4b62-4a7f-ade9-e7a8b430d94d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_ce38482c-2948-4c99-a1b2-7b0efbf41165" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionsProFormaRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_a559be9e-a7d1-4307-a03a-2ccc51957045" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_ce38482c-2948-4c99-a1b2-7b0efbf41165" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_8452fdd8-72f2-4c25-8ef6-19af3d44d747" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_a559be9e-a7d1-4307-a03a-2ccc51957045" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_8452fdd8-72f2-4c25-8ef6-19af3d44d747" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/BusinessCombinationsWondersignDetails" xlink:type="simple" xlink:href="gct-20231231.xsd#BusinessCombinationsWondersignDetails"/>
  <link:definitionLink xlink:role="http://gig.com/role/BusinessCombinationsWondersignDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_e24e605f-a851-4d80-8a6e-361f50fe1ed2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable_87bbdf33-6c54-4e79-b86c-fcb014fdb227" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_e24e605f-a851-4d80-8a6e-361f50fe1ed2" xlink:to="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable_87bbdf33-6c54-4e79-b86c-fcb014fdb227" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_c86a65a9-a6c6-485b-aebe-a01542c17b08" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable_87bbdf33-6c54-4e79-b86c-fcb014fdb227" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_c86a65a9-a6c6-485b-aebe-a01542c17b08" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_c86a65a9-a6c6-485b-aebe-a01542c17b08_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_c86a65a9-a6c6-485b-aebe-a01542c17b08" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_c86a65a9-a6c6-485b-aebe-a01542c17b08_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_e72901c9-0e3b-4e71-bdf6-a3a3eacb87c2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_c86a65a9-a6c6-485b-aebe-a01542c17b08" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_e72901c9-0e3b-4e71-bdf6-a3a3eacb87c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_WondersignMember_fd8f3fbd-1fc2-4951-bc54-c63a1525a943" xlink:href="gct-20231231.xsd#gct_WondersignMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_e72901c9-0e3b-4e71-bdf6-a3a3eacb87c2" xlink:to="loc_gct_WondersignMember_fd8f3fbd-1fc2-4951-bc54-c63a1525a943" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_12b80435-8ef8-40e2-97f6-449eb42b55c9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_e24e605f-a851-4d80-8a6e-361f50fe1ed2" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_12b80435-8ef8-40e2-97f6-449eb42b55c9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_46dd4ec3-024b-457a-a91c-798dd75064ef" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_e24e605f-a851-4d80-8a6e-361f50fe1ed2" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_46dd4ec3-024b-457a-a91c-798dd75064ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_f8f0f24c-ab1f-42dc-ab68-10f00ad1f158" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_e24e605f-a851-4d80-8a6e-361f50fe1ed2" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_f8f0f24c-ab1f-42dc-ab68-10f00ad1f158" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_d22da32e-4daa-4728-bfec-fcd9d253d26c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_e24e605f-a851-4d80-8a6e-361f50fe1ed2" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_d22da32e-4daa-4728-bfec-fcd9d253d26c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_efa3d151-3fe4-4793-9003-12b6db2b2dcf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_e24e605f-a851-4d80-8a6e-361f50fe1ed2" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_efa3d151-3fe4-4793-9003-12b6db2b2dcf" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_122b4a34-3ced-4785-8b8f-3cd1555eb7a7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_e24e605f-a851-4d80-8a6e-361f50fe1ed2" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_122b4a34-3ced-4785-8b8f-3cd1555eb7a7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_d5436b63-118a-49ab-9dda-54d6929264fb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_e24e605f-a851-4d80-8a6e-361f50fe1ed2" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_d5436b63-118a-49ab-9dda-54d6929264fb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesDeferredRevenue_d990c386-5f41-4efb-9ded-7497de3bc784" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesDeferredRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_e24e605f-a851-4d80-8a6e-361f50fe1ed2" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesDeferredRevenue_d990c386-5f41-4efb-9ded-7497de3bc784" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities_1624b0a2-f7a3-4022-8e64-360b32f1f18a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_e24e605f-a851-4d80-8a6e-361f50fe1ed2" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities_1624b0a2-f7a3-4022-8e64-360b32f1f18a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities_c7d1ede4-43a3-4b75-bee9-0b7004f68adc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_e24e605f-a851-4d80-8a6e-361f50fe1ed2" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities_c7d1ede4-43a3-4b75-bee9-0b7004f68adc" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet_02f5e59a-c6c8-4970-81b8-9982bfabb44b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_e24e605f-a851-4d80-8a6e-361f50fe1ed2" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet_02f5e59a-c6c8-4970-81b8-9982bfabb44b" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_b177d887-d09d-4b2e-a478-054401439920" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_e24e605f-a851-4d80-8a6e-361f50fe1ed2" xlink:to="loc_us-gaap_Goodwill_b177d887-d09d-4b2e-a478-054401439920" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_ea7f5164-9196-4e7b-bc58-c9b3c9071231" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_e24e605f-a851-4d80-8a6e-361f50fe1ed2" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_ea7f5164-9196-4e7b-bc58-c9b3c9071231" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/PropertyandEquipmentNetScheduleofPropertyandEquipmentNetDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#PropertyandEquipmentNetScheduleofPropertyandEquipmentNetDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/PropertyandEquipmentNetScheduleofPropertyandEquipmentNetDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_a875a787-f9d7-42f8-978c-8c89b7e292d2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_7f5a883a-4ee2-4c70-a7c3-3784ecfa4932" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_a875a787-f9d7-42f8-978c-8c89b7e292d2" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_7f5a883a-4ee2-4c70-a7c3-3784ecfa4932" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_0a4dfbd0-a658-42f1-bbc1-4e295e4fe273" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_7f5a883a-4ee2-4c70-a7c3-3784ecfa4932" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_0a4dfbd0-a658-42f1-bbc1-4e295e4fe273" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_0a4dfbd0-a658-42f1-bbc1-4e295e4fe273_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_0a4dfbd0-a658-42f1-bbc1-4e295e4fe273" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_0a4dfbd0-a658-42f1-bbc1-4e295e4fe273_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_674770a6-74f2-4c34-bc53-2d2b33cf0c3e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_0a4dfbd0-a658-42f1-bbc1-4e295e4fe273" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_674770a6-74f2-4c34-bc53-2d2b33cf0c3e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_OfficeAndOtherEquipmentMember_f9e8e7f3-7e73-4211-a064-4727c19e9a3e" xlink:href="gct-20231231.xsd#gct_OfficeAndOtherEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_674770a6-74f2-4c34-bc53-2d2b33cf0c3e" xlink:to="loc_gct_OfficeAndOtherEquipmentMember_f9e8e7f3-7e73-4211-a064-4727c19e9a3e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VehiclesMember_e0e2abcd-db43-410a-82b9-b736d23b2af4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_VehiclesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_674770a6-74f2-4c34-bc53-2d2b33cf0c3e" xlink:to="loc_us-gaap_VehiclesMember_e0e2abcd-db43-410a-82b9-b736d23b2af4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_LogisticsWarehouseAndOtherHeavyEquipmentMember_27bb6209-3057-49c3-a121-40b15ba33061" xlink:href="gct-20231231.xsd#gct_LogisticsWarehouseAndOtherHeavyEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_674770a6-74f2-4c34-bc53-2d2b33cf0c3e" xlink:to="loc_gct_LogisticsWarehouseAndOtherHeavyEquipmentMember_27bb6209-3057-49c3-a121-40b15ba33061" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_b9ab449f-050b-4b68-9519-3e879b722588" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_a875a787-f9d7-42f8-978c-8c89b7e292d2" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_b9ab449f-050b-4b68-9519-3e879b722588" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_d5c0183f-b8b2-4dc9-b6b2-1f6be1b2d245" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_a875a787-f9d7-42f8-978c-8c89b7e292d2" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_d5c0183f-b8b2-4dc9-b6b2-1f6be1b2d245" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_dc9f2701-c7c0-4dc5-a7de-2f76cfc80d86" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_a875a787-f9d7-42f8-978c-8c89b7e292d2" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_dc9f2701-c7c0-4dc5-a7de-2f76cfc80d86" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/PropertyandEquipmentNetScheduleofCarryingAmountofPropertyandEquipmentNetAcquiredUnderCapitalAssetsDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#PropertyandEquipmentNetScheduleofCarryingAmountofPropertyandEquipmentNetAcquiredUnderCapitalAssetsDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/PropertyandEquipmentNetScheduleofCarryingAmountofPropertyandEquipmentNetAcquiredUnderCapitalAssetsDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_gct_ScheduleOfPropertyPlantAndEquipmentUnderCapitalLeasesLineItems_b703f2b3-e0a5-4548-9549-0517734907ea" xlink:href="gct-20231231.xsd#gct_ScheduleOfPropertyPlantAndEquipmentUnderCapitalLeasesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ScheduleOfPropertyPlantAndEquipmentUnderCapitalLeasesTable_4d3fe662-bfb4-4dbc-afb1-071438b01ef0" xlink:href="gct-20231231.xsd#gct_ScheduleOfPropertyPlantAndEquipmentUnderCapitalLeasesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_gct_ScheduleOfPropertyPlantAndEquipmentUnderCapitalLeasesLineItems_b703f2b3-e0a5-4548-9549-0517734907ea" xlink:to="loc_gct_ScheduleOfPropertyPlantAndEquipmentUnderCapitalLeasesTable_4d3fe662-bfb4-4dbc-afb1-071438b01ef0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_8f298d9a-e592-49c5-8244-179012f0596f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_ScheduleOfPropertyPlantAndEquipmentUnderCapitalLeasesTable_4d3fe662-bfb4-4dbc-afb1-071438b01ef0" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_8f298d9a-e592-49c5-8244-179012f0596f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_8f298d9a-e592-49c5-8244-179012f0596f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_8f298d9a-e592-49c5-8244-179012f0596f" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_8f298d9a-e592-49c5-8244-179012f0596f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_27ea2014-a65d-44cb-b732-6f24d7c2df3a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_8f298d9a-e592-49c5-8244-179012f0596f" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_27ea2014-a65d-44cb-b732-6f24d7c2df3a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_LogisticsWarehouseAndOtherHeavyEquipmentMember_2f6e6d57-936f-458d-baec-e9b2fd0461d1" xlink:href="gct-20231231.xsd#gct_LogisticsWarehouseAndOtherHeavyEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_27ea2014-a65d-44cb-b732-6f24d7c2df3a" xlink:to="loc_gct_LogisticsWarehouseAndOtherHeavyEquipmentMember_2f6e6d57-936f-458d-baec-e9b2fd0461d1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PropertyPlantAndEquipmentUnderCapitalLeasesGross_1e09ce82-b3ea-4554-aede-d60af0f63b1f" xlink:href="gct-20231231.xsd#gct_PropertyPlantAndEquipmentUnderCapitalLeasesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfPropertyPlantAndEquipmentUnderCapitalLeasesLineItems_b703f2b3-e0a5-4548-9549-0517734907ea" xlink:to="loc_gct_PropertyPlantAndEquipmentUnderCapitalLeasesGross_1e09ce82-b3ea-4554-aede-d60af0f63b1f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PropertyPlantAndEquipmentUnderCapitalLeasesAccumulatedDepreciation_3562d116-5ab0-4cdf-926d-e616b67f7e0b" xlink:href="gct-20231231.xsd#gct_PropertyPlantAndEquipmentUnderCapitalLeasesAccumulatedDepreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfPropertyPlantAndEquipmentUnderCapitalLeasesLineItems_b703f2b3-e0a5-4548-9549-0517734907ea" xlink:to="loc_gct_PropertyPlantAndEquipmentUnderCapitalLeasesAccumulatedDepreciation_3562d116-5ab0-4cdf-926d-e616b67f7e0b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PropertyPlantAndEquipmentUnderCapitalLeasesNet_9300f5cc-e9b9-48e5-8988-daa086c027ba" xlink:href="gct-20231231.xsd#gct_PropertyPlantAndEquipmentUnderCapitalLeasesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfPropertyPlantAndEquipmentUnderCapitalLeasesLineItems_b703f2b3-e0a5-4548-9549-0517734907ea" xlink:to="loc_gct_PropertyPlantAndEquipmentUnderCapitalLeasesNet_9300f5cc-e9b9-48e5-8988-daa086c027ba" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/PropertyandEquipmentNetScheduleofDepreciationExpensesonPropertyandEquipmentDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#PropertyandEquipmentNetScheduleofDepreciationExpensesonPropertyandEquipmentDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/PropertyandEquipmentNetScheduleofDepreciationExpensesonPropertyandEquipmentDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_gct_ScheduleOfDepreciationExpensesOnPropertyPlantAndEquipmentLineItems_03ca4726-1f3e-40b0-b9f0-6cbcc277d910" xlink:href="gct-20231231.xsd#gct_ScheduleOfDepreciationExpensesOnPropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ScheduleOfDepreciationExpensesOnPropertyPlantAndEquipmentTable_6d06d098-d966-4f05-8b67-d60e830b10cd" xlink:href="gct-20231231.xsd#gct_ScheduleOfDepreciationExpensesOnPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_gct_ScheduleOfDepreciationExpensesOnPropertyPlantAndEquipmentLineItems_03ca4726-1f3e-40b0-b9f0-6cbcc277d910" xlink:to="loc_gct_ScheduleOfDepreciationExpensesOnPropertyPlantAndEquipmentTable_6d06d098-d966-4f05-8b67-d60e830b10cd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_72626350-ed12-4a13-9b28-013ad53480e8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_ScheduleOfDepreciationExpensesOnPropertyPlantAndEquipmentTable_6d06d098-d966-4f05-8b67-d60e830b10cd" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_72626350-ed12-4a13-9b28-013ad53480e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_72626350-ed12-4a13-9b28-013ad53480e8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_72626350-ed12-4a13-9b28-013ad53480e8" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_72626350-ed12-4a13-9b28-013ad53480e8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_a03f0dd6-4ad7-47ae-aa57-715d15a83985" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_72626350-ed12-4a13-9b28-013ad53480e8" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_a03f0dd6-4ad7-47ae-aa57-715d15a83985" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_5f6d670b-8f5b-441a-9953-2bfa8cc65458" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_a03f0dd6-4ad7-47ae-aa57-715d15a83985" xlink:to="loc_us-gaap_CostOfSalesMember_5f6d670b-8f5b-441a-9953-2bfa8cc65458" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_34dec5f9-b3d0-4d9f-9670-607fbb48b093" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_a03f0dd6-4ad7-47ae-aa57-715d15a83985" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_34dec5f9-b3d0-4d9f-9670-607fbb48b093" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_04b092ab-d385-47ea-b66f-c1ff189c7677" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ResearchAndDevelopmentExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_a03f0dd6-4ad7-47ae-aa57-715d15a83985" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_04b092ab-d385-47ea-b66f-c1ff189c7677" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassAccumulatedDeprecation_f36a3ee8-593f-4c0a-80ed-4d4cb057161d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassAccumulatedDeprecation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfDepreciationExpensesOnPropertyPlantAndEquipmentLineItems_03ca4726-1f3e-40b0-b9f0-6cbcc277d910" xlink:to="loc_us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassAccumulatedDeprecation_f36a3ee8-593f-4c0a-80ed-4d4cb057161d" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/GoodwillandIntangibleAssetsScheduleofAcquiredFiniteLivedIntangibleAssetsbyMajorClassDetails" xlink:type="simple" xlink:href="gct-20231231.xsd#GoodwillandIntangibleAssetsScheduleofAcquiredFiniteLivedIntangibleAssetsbyMajorClassDetails"/>
  <link:definitionLink xlink:role="http://gig.com/role/GoodwillandIntangibleAssetsScheduleofAcquiredFiniteLivedIntangibleAssetsbyMajorClassDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_747cb319-5f3d-4a3a-ba0d-f9e53561d38e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_38239578-eb57-4260-ae29-256826cc0151" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_747cb319-5f3d-4a3a-ba0d-f9e53561d38e" xlink:to="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_38239578-eb57-4260-ae29-256826cc0151" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_00711a9d-8d9e-4122-83d8-3481af4c5a95" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_38239578-eb57-4260-ae29-256826cc0151" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_00711a9d-8d9e-4122-83d8-3481af4c5a95" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_00711a9d-8d9e-4122-83d8-3481af4c5a95_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_00711a9d-8d9e-4122-83d8-3481af4c5a95" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_00711a9d-8d9e-4122-83d8-3481af4c5a95_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f804c16e-d8c9-4354-b28d-9e0ae95a0f20" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_00711a9d-8d9e-4122-83d8-3481af4c5a95" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f804c16e-d8c9-4354-b28d-9e0ae95a0f20" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_775d767e-3099-46a8-8d06-b1e1cda6bafe" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f804c16e-d8c9-4354-b28d-9e0ae95a0f20" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_775d767e-3099-46a8-8d06-b1e1cda6bafe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_dbe4ae1e-b1aa-4b3b-b1a1-73498d240430" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f804c16e-d8c9-4354-b28d-9e0ae95a0f20" xlink:to="loc_us-gaap_CustomerRelationshipsMember_dbe4ae1e-b1aa-4b3b-b1a1-73498d240430" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_63c059f4-5dfa-46d6-b26e-74c885ff44f3" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_38239578-eb57-4260-ae29-256826cc0151" xlink:to="loc_srt_RangeAxis_63c059f4-5dfa-46d6-b26e-74c885ff44f3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_63c059f4-5dfa-46d6-b26e-74c885ff44f3_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_63c059f4-5dfa-46d6-b26e-74c885ff44f3" xlink:to="loc_srt_RangeMember_63c059f4-5dfa-46d6-b26e-74c885ff44f3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_b6ef06bf-5081-425c-a2b4-e5e7fd1eb187" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_63c059f4-5dfa-46d6-b26e-74c885ff44f3" xlink:to="loc_srt_RangeMember_b6ef06bf-5081-425c-a2b4-e5e7fd1eb187" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_e9770663-d991-4f14-a70c-1425a11b213a" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_b6ef06bf-5081-425c-a2b4-e5e7fd1eb187" xlink:to="loc_srt_MinimumMember_e9770663-d991-4f14-a70c-1425a11b213a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_78fc2795-503c-4b8a-9abf-f7b23a89a1f8" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_b6ef06bf-5081-425c-a2b4-e5e7fd1eb187" xlink:to="loc_srt_MaximumMember_78fc2795-503c-4b8a-9abf-f7b23a89a1f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_f1e36156-e1aa-417e-93d2-097e44e26e8a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_747cb319-5f3d-4a3a-ba0d-f9e53561d38e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_f1e36156-e1aa-417e-93d2-097e44e26e8a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_093bd073-a085-45c1-8910-e782ae089a79" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_747cb319-5f3d-4a3a-ba0d-f9e53561d38e" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_093bd073-a085-45c1-8910-e782ae089a79" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinitelivedIntangibleAssetsAcquired1_4172b3f2-5dcb-4169-ad44-5735a7608274" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FinitelivedIntangibleAssetsAcquired1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_747cb319-5f3d-4a3a-ba0d-f9e53561d38e" xlink:to="loc_us-gaap_FinitelivedIntangibleAssetsAcquired1_4172b3f2-5dcb-4169-ad44-5735a7608274" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_6a8bd283-511f-424b-a901-70e64c04abf7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_747cb319-5f3d-4a3a-ba0d-f9e53561d38e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_6a8bd283-511f-424b-a901-70e64c04abf7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_d49ea3b9-a5a7-4d93-a7a9-91bd65596743" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_747cb319-5f3d-4a3a-ba0d-f9e53561d38e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_d49ea3b9-a5a7-4d93-a7a9-91bd65596743" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/BorrowingsAdditionalInformationDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#BorrowingsAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/BorrowingsAdditionalInformationDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_315df9f1-f746-4e9b-a5ab-eff858d4af9d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_2c454a84-6645-48be-9436-35ab76e9dd06" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_315df9f1-f746-4e9b-a5ab-eff858d4af9d" xlink:to="loc_us-gaap_DebtInstrumentTable_2c454a84-6645-48be-9436-35ab76e9dd06" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityAxis_5616dcc9-eaee-475a-a188-821408a50777" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_2c454a84-6645-48be-9436-35ab76e9dd06" xlink:to="loc_us-gaap_LineOfCreditFacilityAxis_5616dcc9-eaee-475a-a188-821408a50777" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLenderDomain_5616dcc9-eaee-475a-a188-821408a50777_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityLenderDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LineOfCreditFacilityAxis_5616dcc9-eaee-475a-a188-821408a50777" xlink:to="loc_us-gaap_LineOfCreditFacilityLenderDomain_5616dcc9-eaee-475a-a188-821408a50777_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLenderDomain_4b5721b3-ec28-426f-bf85-a50e59fb436a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityLenderDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LineOfCreditFacilityAxis_5616dcc9-eaee-475a-a188-821408a50777" xlink:to="loc_us-gaap_LineOfCreditFacilityLenderDomain_4b5721b3-ec28-426f-bf85-a50e59fb436a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_MIZUHOBankMember_467f99b3-68ca-45ff-9eaf-ea7a2eb50b3b" xlink:href="gct-20231231.xsd#gct_MIZUHOBankMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLenderDomain_4b5721b3-ec28-426f-bf85-a50e59fb436a" xlink:to="loc_gct_MIZUHOBankMember_467f99b3-68ca-45ff-9eaf-ea7a2eb50b3b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_192198d3-9e35-4fe0-a8a1-18043825b4ff" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_2c454a84-6645-48be-9436-35ab76e9dd06" xlink:to="loc_us-gaap_DebtInstrumentAxis_192198d3-9e35-4fe0-a8a1-18043825b4ff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_192198d3-9e35-4fe0-a8a1-18043825b4ff_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_192198d3-9e35-4fe0-a8a1-18043825b4ff" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_192198d3-9e35-4fe0-a8a1-18043825b4ff_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_39c940b2-3b4c-4fdc-a5b6-323bbe42c02a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_192198d3-9e35-4fe0-a8a1-18043825b4ff" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_39c940b2-3b4c-4fdc-a5b6-323bbe42c02a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_LongTermLoanOneMember_42a981a1-17e8-4e59-93f6-94174e4453e3" xlink:href="gct-20231231.xsd#gct_LongTermLoanOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_39c940b2-3b4c-4fdc-a5b6-323bbe42c02a" xlink:to="loc_gct_LongTermLoanOneMember_42a981a1-17e8-4e59-93f6-94174e4453e3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_LongTermLoanTwoMember_07a6d6cc-866a-46b5-a2ea-505804efcc75" xlink:href="gct-20231231.xsd#gct_LongTermLoanTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_39c940b2-3b4c-4fdc-a5b6-323bbe42c02a" xlink:to="loc_gct_LongTermLoanTwoMember_07a6d6cc-866a-46b5-a2ea-505804efcc75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTerm_8819764f-e7c3-493e-b73b-2929d2c7b328" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_315df9f1-f746-4e9b-a5ab-eff858d4af9d" xlink:to="loc_us-gaap_DebtInstrumentTerm_8819764f-e7c3-493e-b73b-2929d2c7b328" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_bfe81d8c-799e-4e28-bdc4-1811a598d1cf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_315df9f1-f746-4e9b-a5ab-eff858d4af9d" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_bfe81d8c-799e-4e28-bdc4-1811a598d1cf" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/AccruedExpensesandOtherCurrentLiabilitiesScheduleofAccruedLiabilitiesDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#AccruedExpensesandOtherCurrentLiabilitiesScheduleofAccruedLiabilitiesDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/AccruedExpensesandOtherCurrentLiabilitiesScheduleofAccruedLiabilitiesDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentLineItems_0403b6ca-a7cb-4272-b2ef-4f4efdc3ed92" xlink:href="gct-20231231.xsd#gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentTable_b67f41fa-f366-494b-b6fb-33af2fdf94e2" xlink:href="gct-20231231.xsd#gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentLineItems_0403b6ca-a7cb-4272-b2ef-4f4efdc3ed92" xlink:to="loc_gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentTable_b67f41fa-f366-494b-b6fb-33af2fdf94e2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_6928bb62-0636-4c3c-876b-214af6571a7f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentTable_b67f41fa-f366-494b-b6fb-33af2fdf94e2" xlink:to="loc_us-gaap_AwardTypeAxis_6928bb62-0636-4c3c-876b-214af6571a7f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6928bb62-0636-4c3c-876b-214af6571a7f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_6928bb62-0636-4c3c-876b-214af6571a7f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6928bb62-0636-4c3c-876b-214af6571a7f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1536dda2-f535-4d5f-bb77-97f006cc6542" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_6928bb62-0636-4c3c-876b-214af6571a7f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1536dda2-f535-4d5f-bb77-97f006cc6542" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_295db4d7-e323-42c8-b006-ed525172d6ae" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1536dda2-f535-4d5f-bb77-97f006cc6542" xlink:to="loc_us-gaap_RestrictedStockMember_295db4d7-e323-42c8-b006-ed525172d6ae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusAxis_3ea356c2-f7fd-4288-974b-64ca37fbe52f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GranteeStatusAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentTable_b67f41fa-f366-494b-b6fb-33af2fdf94e2" xlink:to="loc_us-gaap_GranteeStatusAxis_3ea356c2-f7fd-4288-974b-64ca37fbe52f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_3ea356c2-f7fd-4288-974b-64ca37fbe52f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GranteeStatusAxis_3ea356c2-f7fd-4288-974b-64ca37fbe52f" xlink:to="loc_us-gaap_GranteeStatusDomain_3ea356c2-f7fd-4288-974b-64ca37fbe52f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_aeb6183b-f3b6-4d5d-8528-8eada02513d1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GranteeStatusAxis_3ea356c2-f7fd-4288-974b-64ca37fbe52f" xlink:to="loc_us-gaap_GranteeStatusDomain_aeb6183b-f3b6-4d5d-8528-8eada02513d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_EmployeeAndNonEmployeeMember_3fe3a331-6611-4c00-84c6-a1e084a250b4" xlink:href="gct-20231231.xsd#gct_EmployeeAndNonEmployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_aeb6183b-f3b6-4d5d-8528-8eada02513d1" xlink:to="loc_gct_EmployeeAndNonEmployeeMember_3fe3a331-6611-4c00-84c6-a1e084a250b4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_a1096744-4aa2-4791-ba93-700644d13de5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentTable_b67f41fa-f366-494b-b6fb-33af2fdf94e2" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_a1096744-4aa2-4791-ba93-700644d13de5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_a1096744-4aa2-4791-ba93-700644d13de5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_a1096744-4aa2-4791-ba93-700644d13de5" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_a1096744-4aa2-4791-ba93-700644d13de5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_0e55d71a-71da-4783-baef-a3eda93a82a9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_a1096744-4aa2-4791-ba93-700644d13de5" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_0e55d71a-71da-4783-baef-a3eda93a82a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_AccruedExpensesAndOtherCurrentLiabilitiesMember_905fde15-9a6b-4588-ac5a-93ea8df46e2c" xlink:href="gct-20231231.xsd#gct_AccruedExpensesAndOtherCurrentLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_0e55d71a-71da-4783-baef-a3eda93a82a9" xlink:to="loc_gct_AccruedExpensesAndOtherCurrentLiabilitiesMember_905fde15-9a6b-4588-ac5a-93ea8df46e2c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRefundLiabilityCurrent_38ed5740-7b31-4bcc-8da0-6752ebf03327" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CustomerRefundLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentLineItems_0403b6ca-a7cb-4272-b2ef-4f4efdc3ed92" xlink:to="loc_us-gaap_CustomerRefundLiabilityCurrent_38ed5740-7b31-4bcc-8da0-6752ebf03327" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_CreditCardPayables_309b2c25-24eb-4e83-924e-65b03a5e3c87" xlink:href="gct-20231231.xsd#gct_CreditCardPayables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentLineItems_0403b6ca-a7cb-4272-b2ef-4f4efdc3ed92" xlink:to="loc_gct_CreditCardPayables_309b2c25-24eb-4e83-924e-65b03a5e3c87" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeRelatedLiabilitiesCurrent_83a42fa4-fb30-447c-b537-991e904df869" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeRelatedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentLineItems_0403b6ca-a7cb-4272-b2ef-4f4efdc3ed92" xlink:to="loc_us-gaap_EmployeeRelatedLiabilitiesCurrent_83a42fa4-fb30-447c-b537-991e904df869" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerRefundLiabilityCurrent_11da2451-3e4f-41c0-9a3d-9d94b0d10238" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ContractWithCustomerRefundLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentLineItems_0403b6ca-a7cb-4272-b2ef-4f4efdc3ed92" xlink:to="loc_us-gaap_ContractWithCustomerRefundLiabilityCurrent_11da2451-3e4f-41c0-9a3d-9d94b0d10238" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccrualForTaxesOtherThanIncomeTaxesCurrent_14b148c7-1d20-4e98-850a-e5d19d63afba" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccrualForTaxesOtherThanIncomeTaxesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentLineItems_0403b6ca-a7cb-4272-b2ef-4f4efdc3ed92" xlink:to="loc_us-gaap_AccrualForTaxesOtherThanIncomeTaxesCurrent_14b148c7-1d20-4e98-850a-e5d19d63afba" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseLiabilityCurrent_8ae9bc02-af71-40cc-96dc-e2f635647140" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FinanceLeaseLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentLineItems_0403b6ca-a7cb-4272-b2ef-4f4efdc3ed92" xlink:to="loc_us-gaap_FinanceLeaseLiabilityCurrent_8ae9bc02-af71-40cc-96dc-e2f635647140" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedProfessionalFeesCurrent_dd04eb2c-790e-414a-9707-cf2c52bad910" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccruedProfessionalFeesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentLineItems_0403b6ca-a7cb-4272-b2ef-4f4efdc3ed92" xlink:to="loc_us-gaap_AccruedProfessionalFeesCurrent_dd04eb2c-790e-414a-9707-cf2c52bad910" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ObligationsUnderTheRemorseProtectionProgramCurrent_4975f294-34db-4ae4-ade3-f771920910a9" xlink:href="gct-20231231.xsd#gct_ObligationsUnderTheRemorseProtectionProgramCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentLineItems_0403b6ca-a7cb-4272-b2ef-4f4efdc3ed92" xlink:to="loc_gct_ObligationsUnderTheRemorseProtectionProgramCurrent_4975f294-34db-4ae4-ade3-f771920910a9" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ConsiderationForRestrictedSharesReceivedInAdvanceCurrent_3f55ab85-5e7c-48f5-a55f-243ad752be15" xlink:href="gct-20231231.xsd#gct_ConsiderationForRestrictedSharesReceivedInAdvanceCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentLineItems_0403b6ca-a7cb-4272-b2ef-4f4efdc3ed92" xlink:to="loc_gct_ConsiderationForRestrictedSharesReceivedInAdvanceCurrent_3f55ab85-5e7c-48f5-a55f-243ad752be15" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationLiabilityCurrent_3aecef90-6c55-4bf3-a8d9-7b8bd88c21de" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredCompensationLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentLineItems_0403b6ca-a7cb-4272-b2ef-4f4efdc3ed92" xlink:to="loc_us-gaap_DeferredCompensationLiabilityCurrent_3aecef90-6c55-4bf3-a8d9-7b8bd88c21de" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAccruedLiabilitiesCurrent_3682f82d-3c53-4dcf-b3d8-3781812bd6f2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherAccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentLineItems_0403b6ca-a7cb-4272-b2ef-4f4efdc3ed92" xlink:to="loc_us-gaap_OtherAccruedLiabilitiesCurrent_3682f82d-3c53-4dcf-b3d8-3781812bd6f2" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_c6a6bc08-b81a-476b-9af8-5744a94e583a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentLineItems_0403b6ca-a7cb-4272-b2ef-4f4efdc3ed92" xlink:to="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_c6a6bc08-b81a-476b-9af8-5744a94e583a" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_9baaccdc-3b36-4be6-b5c9-29a882660218" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentLineItems_0403b6ca-a7cb-4272-b2ef-4f4efdc3ed92" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_9baaccdc-3b36-4be6-b5c9-29a882660218" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_8ebe5f07-1a55-43bc-8481-fb0c161433f4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentLineItems_0403b6ca-a7cb-4272-b2ef-4f4efdc3ed92" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_8ebe5f07-1a55-43bc-8481-fb0c161433f4" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationRestrictedStockUnitsRequisiteServicePeriodRecognition_08ba2e57-4683-471e-b2aa-b1faa658f096" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationRestrictedStockUnitsRequisiteServicePeriodRecognition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentLineItems_0403b6ca-a7cb-4272-b2ef-4f4efdc3ed92" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationRestrictedStockUnitsRequisiteServicePeriodRecognition_08ba2e57-4683-471e-b2aa-b1faa658f096" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WorkersCompensationLiabilityCurrent_2e88d97b-f282-4442-b861-90fa6f5b63e0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_WorkersCompensationLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfAccountsPayableAndOtherLiabilitiesDisclosureCurrentLineItems_0403b6ca-a7cb-4272-b2ef-4f4efdc3ed92" xlink:to="loc_us-gaap_WorkersCompensationLiabilityCurrent_2e88d97b-f282-4442-b861-90fa6f5b63e0" xlink:type="arc" order="15"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/PreferredSharesNarrativeSeriesADetails" xlink:type="simple" xlink:href="gct-20231231.xsd#PreferredSharesNarrativeSeriesADetails"/>
  <link:definitionLink xlink:role="http://gig.com/role/PreferredSharesNarrativeSeriesADetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityLineItems_9b79f62c-0193-49a3-94b4-b2b231832748" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityByClassOfStockTable_62892afe-3c75-4c5d-8882-b12a7dbb0230" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquityByClassOfStockTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_TemporaryEquityLineItems_9b79f62c-0193-49a3-94b4-b2b231832748" xlink:to="loc_us-gaap_TemporaryEquityByClassOfStockTable_62892afe-3c75-4c5d-8882-b12a7dbb0230" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_d7f472a2-f8f2-4e25-b0da-ac9734d334d8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_62892afe-3c75-4c5d-8882-b12a7dbb0230" xlink:to="loc_us-gaap_StatementClassOfStockAxis_d7f472a2-f8f2-4e25-b0da-ac9734d334d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_d7f472a2-f8f2-4e25-b0da-ac9734d334d8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_d7f472a2-f8f2-4e25-b0da-ac9734d334d8" xlink:to="loc_us-gaap_ClassOfStockDomain_d7f472a2-f8f2-4e25-b0da-ac9734d334d8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_6ff007ca-5f16-4a19-a2d6-717356686773" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_d7f472a2-f8f2-4e25-b0da-ac9734d334d8" xlink:to="loc_us-gaap_ClassOfStockDomain_6ff007ca-5f16-4a19-a2d6-717356686773" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesAPreferredStockMember_5d881d92-19e1-440f-9706-598444bbdbcd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SeriesAPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_6ff007ca-5f16-4a19-a2d6-717356686773" xlink:to="loc_us-gaap_SeriesAPreferredStockMember_5d881d92-19e1-440f-9706-598444bbdbcd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityAxis_19903e46-223e-4041-987b-1244bb87626a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_62892afe-3c75-4c5d-8882-b12a7dbb0230" xlink:to="loc_us-gaap_LineOfCreditFacilityAxis_19903e46-223e-4041-987b-1244bb87626a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLenderDomain_19903e46-223e-4041-987b-1244bb87626a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityLenderDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LineOfCreditFacilityAxis_19903e46-223e-4041-987b-1244bb87626a" xlink:to="loc_us-gaap_LineOfCreditFacilityLenderDomain_19903e46-223e-4041-987b-1244bb87626a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLenderDomain_76b7c032-e618-4a4a-ae4f-e6ace8c0e1be" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityLenderDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LineOfCreditFacilityAxis_19903e46-223e-4041-987b-1244bb87626a" xlink:to="loc_us-gaap_LineOfCreditFacilityLenderDomain_76b7c032-e618-4a4a-ae4f-e6ace8c0e1be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_DcmIvMember_c477c6c5-8887-403d-8319-df0fcfebfa89" xlink:href="gct-20231231.xsd#gct_DcmIvMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLenderDomain_76b7c032-e618-4a4a-ae4f-e6ace8c0e1be" xlink:to="loc_gct_DcmIvMember_c477c6c5-8887-403d-8319-df0fcfebfa89" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_DcmIvAffiliatesMember_fecad0b1-3b9f-4458-b219-abfdcf0f6e7d" xlink:href="gct-20231231.xsd#gct_DcmIvAffiliatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLenderDomain_76b7c032-e618-4a4a-ae4f-e6ace8c0e1be" xlink:to="loc_gct_DcmIvAffiliatesMember_fecad0b1-3b9f-4458-b219-abfdcf0f6e7d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_DtMember_343b3edb-04dc-4781-8cef-fc8447b41cc5" xlink:href="gct-20231231.xsd#gct_DtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLenderDomain_76b7c032-e618-4a4a-ae4f-e6ace8c0e1be" xlink:to="loc_gct_DtMember_343b3edb-04dc-4781-8cef-fc8447b41cc5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_eb6a00f4-b3a7-415c-9b76-de981451f9d6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_9b79f62c-0193-49a3-94b4-b2b231832748" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_eb6a00f4-b3a7-415c-9b76-de981451f9d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_9464d350-4312-4756-abb7-4cbc8a4067a2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_9b79f62c-0193-49a3-94b4-b2b231832748" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_9464d350-4312-4756-abb7-4cbc8a4067a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockShareSubscriptions_5d5e05ac-f118-4a09-8ec4-6214e23a1ab7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PreferredStockShareSubscriptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_9b79f62c-0193-49a3-94b4-b2b231832748" xlink:to="loc_us-gaap_PreferredStockShareSubscriptions_5d5e05ac-f118-4a09-8ec4-6214e23a1ab7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_14e46dc4-e20f-487d-b32e-8168f1e77f22" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_9b79f62c-0193-49a3-94b4-b2b231832748" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_14e46dc4-e20f-487d-b32e-8168f1e77f22" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesSubscribedButUnissuedValue_47478902-cbcc-4859-81d4-f792ca2f5264" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PreferredStockSharesSubscribedButUnissuedValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_9b79f62c-0193-49a3-94b4-b2b231832748" xlink:to="loc_us-gaap_PreferredStockSharesSubscribedButUnissuedValue_47478902-cbcc-4859-81d4-f792ca2f5264" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtConversionOriginalDebtAmount1_46e5a087-00db-4d8b-bfb9-dfd6f728a648" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtConversionOriginalDebtAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_9b79f62c-0193-49a3-94b4-b2b231832748" xlink:to="loc_us-gaap_DebtConversionOriginalDebtAmount1_46e5a087-00db-4d8b-bfb9-dfd6f728a648" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtConversionConvertedInstrumentSharesIssued1_a30b3a4c-9401-459b-9933-8cf56e4b0ee8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtConversionConvertedInstrumentSharesIssued1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_9b79f62c-0193-49a3-94b4-b2b231832748" xlink:to="loc_us-gaap_DebtConversionConvertedInstrumentSharesIssued1_a30b3a4c-9401-459b-9933-8cf56e4b0ee8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssuedPricePerShare_6ca3fd50-5b59-4a01-94da-b61b8534caae" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharesIssuedPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_9b79f62c-0193-49a3-94b4-b2b231832748" xlink:to="loc_us-gaap_SharesIssuedPricePerShare_6ca3fd50-5b59-4a01-94da-b61b8534caae" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/PreferredSharesNarrativeSeriesBDetails" xlink:type="simple" xlink:href="gct-20231231.xsd#PreferredSharesNarrativeSeriesBDetails"/>
  <link:definitionLink xlink:role="http://gig.com/role/PreferredSharesNarrativeSeriesBDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityLineItems_6d88f8c9-7123-4047-b539-e3f333589ec7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityByClassOfStockTable_c39a3ca5-70d5-4738-8f65-1ceb7581ae28" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquityByClassOfStockTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_TemporaryEquityLineItems_6d88f8c9-7123-4047-b539-e3f333589ec7" xlink:to="loc_us-gaap_TemporaryEquityByClassOfStockTable_c39a3ca5-70d5-4738-8f65-1ceb7581ae28" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_6c10d315-bacb-4f70-b93b-7f3b82e340ea" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_c39a3ca5-70d5-4738-8f65-1ceb7581ae28" xlink:to="loc_us-gaap_StatementClassOfStockAxis_6c10d315-bacb-4f70-b93b-7f3b82e340ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_6c10d315-bacb-4f70-b93b-7f3b82e340ea_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_6c10d315-bacb-4f70-b93b-7f3b82e340ea" xlink:to="loc_us-gaap_ClassOfStockDomain_6c10d315-bacb-4f70-b93b-7f3b82e340ea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_ee9abd52-92c8-4110-84b1-af63a1467c42" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_6c10d315-bacb-4f70-b93b-7f3b82e340ea" xlink:to="loc_us-gaap_ClassOfStockDomain_ee9abd52-92c8-4110-84b1-af63a1467c42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesBPreferredStockMember_118b28ab-6d85-46f2-b006-98a85a1a5d66" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SeriesBPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_ee9abd52-92c8-4110-84b1-af63a1467c42" xlink:to="loc_us-gaap_SeriesBPreferredStockMember_118b28ab-6d85-46f2-b006-98a85a1a5d66" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityAxis_e6a84067-63be-486a-bd2c-4e169a4ef6dd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_c39a3ca5-70d5-4738-8f65-1ceb7581ae28" xlink:to="loc_us-gaap_LineOfCreditFacilityAxis_e6a84067-63be-486a-bd2c-4e169a4ef6dd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLenderDomain_e6a84067-63be-486a-bd2c-4e169a4ef6dd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityLenderDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LineOfCreditFacilityAxis_e6a84067-63be-486a-bd2c-4e169a4ef6dd" xlink:to="loc_us-gaap_LineOfCreditFacilityLenderDomain_e6a84067-63be-486a-bd2c-4e169a4ef6dd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLenderDomain_ee98aa92-65b0-4f1e-a770-1b2942afe874" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityLenderDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LineOfCreditFacilityAxis_e6a84067-63be-486a-bd2c-4e169a4ef6dd" xlink:to="loc_us-gaap_LineOfCreditFacilityLenderDomain_ee98aa92-65b0-4f1e-a770-1b2942afe874" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_DcmIvMember_3fe3a425-119d-480f-b6c6-4f88da629794" xlink:href="gct-20231231.xsd#gct_DcmIvMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLenderDomain_ee98aa92-65b0-4f1e-a770-1b2942afe874" xlink:to="loc_gct_DcmIvMember_3fe3a425-119d-480f-b6c6-4f88da629794" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_DcmIvAffiliatesMember_86ed3223-9205-4590-9a01-5de26f8fbebd" xlink:href="gct-20231231.xsd#gct_DcmIvAffiliatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLenderDomain_ee98aa92-65b0-4f1e-a770-1b2942afe874" xlink:to="loc_gct_DcmIvAffiliatesMember_86ed3223-9205-4590-9a01-5de26f8fbebd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_DtMember_2e3175ba-1c2c-4ee1-918e-fa496e82948a" xlink:href="gct-20231231.xsd#gct_DtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLenderDomain_ee98aa92-65b0-4f1e-a770-1b2942afe874" xlink:to="loc_gct_DtMember_2e3175ba-1c2c-4ee1-918e-fa496e82948a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_e0b6e7d7-4db0-440c-903f-2691216544e9" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_c39a3ca5-70d5-4738-8f65-1ceb7581ae28" xlink:to="loc_srt_TitleOfIndividualAxis_e0b6e7d7-4db0-440c-903f-2691216544e9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_e0b6e7d7-4db0-440c-903f-2691216544e9_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_e0b6e7d7-4db0-440c-903f-2691216544e9" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_e0b6e7d7-4db0-440c-903f-2691216544e9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_123c7200-2dde-49d4-b587-0b700f90802f" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_e0b6e7d7-4db0-440c-903f-2691216544e9" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_123c7200-2dde-49d4-b587-0b700f90802f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_LarryLeiWuMember_f2510131-390f-471c-b7a5-7b19e66243c1" xlink:href="gct-20231231.xsd#gct_LarryLeiWuMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_123c7200-2dde-49d4-b587-0b700f90802f" xlink:to="loc_gct_LarryLeiWuMember_f2510131-390f-471c-b7a5-7b19e66243c1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_57ed4992-a1c6-4c6f-85ec-75e4e9723894" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_6d88f8c9-7123-4047-b539-e3f333589ec7" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_57ed4992-a1c6-4c6f-85ec-75e4e9723894" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_5e6ccdc6-abd1-4e07-a1f1-fd0ee9ac8f8c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_6d88f8c9-7123-4047-b539-e3f333589ec7" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_5e6ccdc6-abd1-4e07-a1f1-fd0ee9ac8f8c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockShareSubscriptions_bdf03f90-02f5-435b-bfaf-c68381f3813e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PreferredStockShareSubscriptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_6d88f8c9-7123-4047-b539-e3f333589ec7" xlink:to="loc_us-gaap_PreferredStockShareSubscriptions_bdf03f90-02f5-435b-bfaf-c68381f3813e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_2fe0d497-8a84-425b-9b58-3fa377a84fa1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_6d88f8c9-7123-4047-b539-e3f333589ec7" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_2fe0d497-8a84-425b-9b58-3fa377a84fa1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesSubscribedButUnissuedValue_2bf74e7b-9be4-4443-82fe-e114546e5f9d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PreferredStockSharesSubscribedButUnissuedValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_6d88f8c9-7123-4047-b539-e3f333589ec7" xlink:to="loc_us-gaap_PreferredStockSharesSubscribedButUnissuedValue_2bf74e7b-9be4-4443-82fe-e114546e5f9d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtConversionOriginalDebtAmount1_36279aed-ebcc-48d8-8d79-311d0dd363b3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtConversionOriginalDebtAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_6d88f8c9-7123-4047-b539-e3f333589ec7" xlink:to="loc_us-gaap_DebtConversionOriginalDebtAmount1_36279aed-ebcc-48d8-8d79-311d0dd363b3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtConversionConvertedInstrumentSharesIssued1_d4dc6570-5a9f-4097-aa1d-43cac0ac9d48" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtConversionConvertedInstrumentSharesIssued1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_6d88f8c9-7123-4047-b539-e3f333589ec7" xlink:to="loc_us-gaap_DebtConversionConvertedInstrumentSharesIssued1_d4dc6570-5a9f-4097-aa1d-43cac0ac9d48" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssuedPricePerShare_a4f29669-79fb-44df-bd38-7fe0a3abd35a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharesIssuedPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_6d88f8c9-7123-4047-b539-e3f333589ec7" xlink:to="loc_us-gaap_SharesIssuedPricePerShare_a4f29669-79fb-44df-bd38-7fe0a3abd35a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_a066479c-b78b-4c3d-a786-921317e0d9cd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_6d88f8c9-7123-4047-b539-e3f333589ec7" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_a066479c-b78b-4c3d-a786-921317e0d9cd" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_b6ce923d-a59b-42fd-a760-502301bfa35c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockRepurchasedDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_6d88f8c9-7123-4047-b539-e3f333589ec7" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_b6ce923d-a59b-42fd-a760-502301bfa35c" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/PreferredSharesNarrativeSeriesCDetails" xlink:type="simple" xlink:href="gct-20231231.xsd#PreferredSharesNarrativeSeriesCDetails"/>
  <link:definitionLink xlink:role="http://gig.com/role/PreferredSharesNarrativeSeriesCDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityLineItems_52fc1233-10d0-40dc-bb31-8144e3904003" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityByClassOfStockTable_9fc23d5d-acf7-4281-a93c-e020cb95831c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquityByClassOfStockTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_TemporaryEquityLineItems_52fc1233-10d0-40dc-bb31-8144e3904003" xlink:to="loc_us-gaap_TemporaryEquityByClassOfStockTable_9fc23d5d-acf7-4281-a93c-e020cb95831c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_AcquireeAxis_c1ce5758-1ed3-4e8a-a4f3-54ee0822b7dd" xlink:href="gct-20231231.xsd#gct_AcquireeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_9fc23d5d-acf7-4281-a93c-e020cb95831c" xlink:to="loc_gct_AcquireeAxis_c1ce5758-1ed3-4e8a-a4f3-54ee0822b7dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_AcquireeDomain_c1ce5758-1ed3-4e8a-a4f3-54ee0822b7dd_default" xlink:href="gct-20231231.xsd#gct_AcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_gct_AcquireeAxis_c1ce5758-1ed3-4e8a-a4f3-54ee0822b7dd" xlink:to="loc_gct_AcquireeDomain_c1ce5758-1ed3-4e8a-a4f3-54ee0822b7dd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_AcquireeDomain_b2f21102-ab0b-4094-a452-1adcd1057564" xlink:href="gct-20231231.xsd#gct_AcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_gct_AcquireeAxis_c1ce5758-1ed3-4e8a-a4f3-54ee0822b7dd" xlink:to="loc_gct_AcquireeDomain_b2f21102-ab0b-4094-a452-1adcd1057564" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_FiredragonHoldingsIncMember_5f4ca6dc-33fa-4495-baa4-6ffd496a3760" xlink:href="gct-20231231.xsd#gct_FiredragonHoldingsIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_AcquireeDomain_b2f21102-ab0b-4094-a452-1adcd1057564" xlink:to="loc_gct_FiredragonHoldingsIncMember_5f4ca6dc-33fa-4495-baa4-6ffd496a3760" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_DcmFourMember_1c1fe774-1032-4499-9ffe-0213a10b99bc" xlink:href="gct-20231231.xsd#gct_DcmFourMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_AcquireeDomain_b2f21102-ab0b-4094-a452-1adcd1057564" xlink:to="loc_gct_DcmFourMember_1c1fe774-1032-4499-9ffe-0213a10b99bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_DcmFourAffiliatesMember_defc6dfd-73eb-4d46-95a0-025bbc105430" xlink:href="gct-20231231.xsd#gct_DcmFourAffiliatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_AcquireeDomain_b2f21102-ab0b-4094-a452-1adcd1057564" xlink:to="loc_gct_DcmFourAffiliatesMember_defc6dfd-73eb-4d46-95a0-025bbc105430" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_DtECommerceInvestmentLimitedMember_858225b3-217e-4924-a0a6-4d563b7a6c54" xlink:href="gct-20231231.xsd#gct_DtECommerceInvestmentLimitedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_AcquireeDomain_b2f21102-ab0b-4094-a452-1adcd1057564" xlink:to="loc_gct_DtECommerceInvestmentLimitedMember_858225b3-217e-4924-a0a6-4d563b7a6c54" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_6c552a7e-aa3e-4fcb-9a7f-c8ea3ec623f0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_9fc23d5d-acf7-4281-a93c-e020cb95831c" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_6c552a7e-aa3e-4fcb-9a7f-c8ea3ec623f0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_6c552a7e-aa3e-4fcb-9a7f-c8ea3ec623f0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_6c552a7e-aa3e-4fcb-9a7f-c8ea3ec623f0" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_6c552a7e-aa3e-4fcb-9a7f-c8ea3ec623f0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8fd89344-bbb0-4905-8edc-7798f2e98d83" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_6c552a7e-aa3e-4fcb-9a7f-c8ea3ec623f0" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8fd89344-bbb0-4905-8edc-7798f2e98d83" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ComptreeInternationalLimitedMember_5bd3a79a-523e-4f5e-a0cd-667e23721adc" xlink:href="gct-20231231.xsd#gct_ComptreeInternationalLimitedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8fd89344-bbb0-4905-8edc-7798f2e98d83" xlink:to="loc_gct_ComptreeInternationalLimitedMember_5bd3a79a-523e-4f5e-a0cd-667e23721adc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_2e450478-5cac-4bbc-b31a-9116bb7c2fa4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_9fc23d5d-acf7-4281-a93c-e020cb95831c" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_2e450478-5cac-4bbc-b31a-9116bb7c2fa4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_2e450478-5cac-4bbc-b31a-9116bb7c2fa4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_2e450478-5cac-4bbc-b31a-9116bb7c2fa4" xlink:to="loc_us-gaap_EquityComponentDomain_2e450478-5cac-4bbc-b31a-9116bb7c2fa4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_0ec46163-baf7-4e03-90e1-a072bfdcb205" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_2e450478-5cac-4bbc-b31a-9116bb7c2fa4" xlink:to="loc_us-gaap_EquityComponentDomain_0ec46163-baf7-4e03-90e1-a072bfdcb205" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_951f7bbf-7843-49f0-b52b-1ee4f8a05e17" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_0ec46163-baf7-4e03-90e1-a072bfdcb205" xlink:to="loc_us-gaap_CommonStockMember_951f7bbf-7843-49f0-b52b-1ee4f8a05e17" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockMember_28a325b7-2e90-44b2-9605-c911939ce9f3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_0ec46163-baf7-4e03-90e1-a072bfdcb205" xlink:to="loc_us-gaap_PreferredStockMember_28a325b7-2e90-44b2-9605-c911939ce9f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_48d1b7f7-492a-4584-a223-b7e5dfced003" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_9fc23d5d-acf7-4281-a93c-e020cb95831c" xlink:to="loc_us-gaap_StatementClassOfStockAxis_48d1b7f7-492a-4584-a223-b7e5dfced003" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_48d1b7f7-492a-4584-a223-b7e5dfced003_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_48d1b7f7-492a-4584-a223-b7e5dfced003" xlink:to="loc_us-gaap_ClassOfStockDomain_48d1b7f7-492a-4584-a223-b7e5dfced003_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_d4a87012-7bdd-406e-80ed-080994aa7210" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_48d1b7f7-492a-4584-a223-b7e5dfced003" xlink:to="loc_us-gaap_ClassOfStockDomain_d4a87012-7bdd-406e-80ed-080994aa7210" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesCPreferredStockMember_7c40d00d-5a2c-4e9a-8bd2-f9c1ff29310e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SeriesCPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_d4a87012-7bdd-406e-80ed-080994aa7210" xlink:to="loc_us-gaap_SeriesCPreferredStockMember_7c40d00d-5a2c-4e9a-8bd2-f9c1ff29310e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_621cd9e6-4b3c-4401-b836-554aec86cdb0" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_9fc23d5d-acf7-4281-a93c-e020cb95831c" xlink:to="loc_srt_TitleOfIndividualAxis_621cd9e6-4b3c-4401-b836-554aec86cdb0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_621cd9e6-4b3c-4401-b836-554aec86cdb0_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_621cd9e6-4b3c-4401-b836-554aec86cdb0" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_621cd9e6-4b3c-4401-b836-554aec86cdb0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_dcd22af4-fec2-4a02-be52-8be328906028" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_621cd9e6-4b3c-4401-b836-554aec86cdb0" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_dcd22af4-fec2-4a02-be52-8be328906028" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_LianyaPanMember_5384d642-3881-42f9-be4a-89a9fa1734e9" xlink:href="gct-20231231.xsd#gct_LianyaPanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_dcd22af4-fec2-4a02-be52-8be328906028" xlink:to="loc_gct_LianyaPanMember_5384d642-3881-42f9-be4a-89a9fa1734e9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_f1d0fc6d-9214-48c7-aed8-e53872558019" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_52fc1233-10d0-40dc-bb31-8144e3904003" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_f1d0fc6d-9214-48c7-aed8-e53872558019" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_ed9db934-8bb0-4912-9436-61568f951527" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_52fc1233-10d0-40dc-bb31-8144e3904003" xlink:to="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_ed9db934-8bb0-4912-9436-61568f951527" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/PreferredSharesNarrativeSeriesDDetails" xlink:type="simple" xlink:href="gct-20231231.xsd#PreferredSharesNarrativeSeriesDDetails"/>
  <link:definitionLink xlink:role="http://gig.com/role/PreferredSharesNarrativeSeriesDDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityLineItems_94b60786-4da5-41e0-8cc4-94ee2335e54e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityByClassOfStockTable_63b93942-a4ca-4f23-abb7-e41ecf904600" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquityByClassOfStockTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_TemporaryEquityLineItems_94b60786-4da5-41e0-8cc4-94ee2335e54e" xlink:to="loc_us-gaap_TemporaryEquityByClassOfStockTable_63b93942-a4ca-4f23-abb7-e41ecf904600" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PreferredStockOneAxis_80e3a752-221d-4c4b-8b94-3cddb098a4ed" xlink:href="gct-20231231.xsd#gct_PreferredStockOneAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_63b93942-a4ca-4f23-abb7-e41ecf904600" xlink:to="loc_gct_PreferredStockOneAxis_80e3a752-221d-4c4b-8b94-3cddb098a4ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PreferredStockOneDomain_80e3a752-221d-4c4b-8b94-3cddb098a4ed_default" xlink:href="gct-20231231.xsd#gct_PreferredStockOneDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_gct_PreferredStockOneAxis_80e3a752-221d-4c4b-8b94-3cddb098a4ed" xlink:to="loc_gct_PreferredStockOneDomain_80e3a752-221d-4c4b-8b94-3cddb098a4ed_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PreferredStockOneDomain_856880eb-3f15-44ff-b7e3-812b126fb918" xlink:href="gct-20231231.xsd#gct_PreferredStockOneDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_gct_PreferredStockOneAxis_80e3a752-221d-4c4b-8b94-3cddb098a4ed" xlink:to="loc_gct_PreferredStockOneDomain_856880eb-3f15-44ff-b7e3-812b126fb918" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_SeriesDConvertiblePreferredStockMember_788476a1-4c56-4701-a76f-b09738f110c4" xlink:href="gct-20231231.xsd#gct_SeriesDConvertiblePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_PreferredStockOneDomain_856880eb-3f15-44ff-b7e3-812b126fb918" xlink:to="loc_gct_SeriesDConvertiblePreferredStockMember_788476a1-4c56-4701-a76f-b09738f110c4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_InvestorAxis_e89842c9-6c6c-49ea-9e0f-397ff18e3334" xlink:href="gct-20231231.xsd#gct_InvestorAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_63b93942-a4ca-4f23-abb7-e41ecf904600" xlink:to="loc_gct_InvestorAxis_e89842c9-6c6c-49ea-9e0f-397ff18e3334" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_InvestorDomain_e89842c9-6c6c-49ea-9e0f-397ff18e3334_default" xlink:href="gct-20231231.xsd#gct_InvestorDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_gct_InvestorAxis_e89842c9-6c6c-49ea-9e0f-397ff18e3334" xlink:to="loc_gct_InvestorDomain_e89842c9-6c6c-49ea-9e0f-397ff18e3334_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_InvestorDomain_3312be3b-1202-4a3f-bf93-b7c2988385ce" xlink:href="gct-20231231.xsd#gct_InvestorDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_gct_InvestorAxis_e89842c9-6c6c-49ea-9e0f-397ff18e3334" xlink:to="loc_gct_InvestorDomain_3312be3b-1202-4a3f-bf93-b7c2988385ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_HongKongRedStarMacallineUniversalMachineHoldingsMember_4ea62f94-cd19-4f59-a3d5-ad2ea40343b8" xlink:href="gct-20231231.xsd#gct_HongKongRedStarMacallineUniversalMachineHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_InvestorDomain_3312be3b-1202-4a3f-bf93-b7c2988385ce" xlink:to="loc_gct_HongKongRedStarMacallineUniversalMachineHoldingsMember_4ea62f94-cd19-4f59-a3d5-ad2ea40343b8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_45dff895-1d7e-4111-945d-0aebde690c57" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_63b93942-a4ca-4f23-abb7-e41ecf904600" xlink:to="loc_us-gaap_StatementClassOfStockAxis_45dff895-1d7e-4111-945d-0aebde690c57" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_45dff895-1d7e-4111-945d-0aebde690c57_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_45dff895-1d7e-4111-945d-0aebde690c57" xlink:to="loc_us-gaap_ClassOfStockDomain_45dff895-1d7e-4111-945d-0aebde690c57_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_9bbabadc-d6f3-4719-94f4-fe95100c6030" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_45dff895-1d7e-4111-945d-0aebde690c57" xlink:to="loc_us-gaap_ClassOfStockDomain_9bbabadc-d6f3-4719-94f4-fe95100c6030" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertiblePreferredStockMember_63f396f7-4aff-4877-a738-603a1475dbfb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConvertiblePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_9bbabadc-d6f3-4719-94f4-fe95100c6030" xlink:to="loc_us-gaap_ConvertiblePreferredStockMember_63f396f7-4aff-4877-a738-603a1475dbfb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_240ef654-50e9-424c-b181-801de849faeb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_94b60786-4da5-41e0-8cc4-94ee2335e54e" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_240ef654-50e9-424c-b181-801de849faeb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssuedPricePerShare_a2c48128-5a15-40be-af00-000d20cd0990" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharesIssuedPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_94b60786-4da5-41e0-8cc4-94ee2335e54e" xlink:to="loc_us-gaap_SharesIssuedPricePerShare_a2c48128-5a15-40be-af00-000d20cd0990" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfConvertiblePreferredStock_81b997a4-e78f-4ff1-ad5c-9357c5cf36ba" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromIssuanceOfConvertiblePreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_94b60786-4da5-41e0-8cc4-94ee2335e54e" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfConvertiblePreferredStock_81b997a4-e78f-4ff1-ad5c-9357c5cf36ba" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/PreferredSharesNarrativeSeriesEDetails" xlink:type="simple" xlink:href="gct-20231231.xsd#PreferredSharesNarrativeSeriesEDetails"/>
  <link:definitionLink xlink:role="http://gig.com/role/PreferredSharesNarrativeSeriesEDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityLineItems_b73d62d3-eb76-40b5-b114-60477dc1dd38" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityByClassOfStockTable_0a9ff259-7d14-4d97-beb0-98d0314b56fd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquityByClassOfStockTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_TemporaryEquityLineItems_b73d62d3-eb76-40b5-b114-60477dc1dd38" xlink:to="loc_us-gaap_TemporaryEquityByClassOfStockTable_0a9ff259-7d14-4d97-beb0-98d0314b56fd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PreferredStockOneAxis_c0c3161d-bfda-4264-9080-6ce7a5dc544a" xlink:href="gct-20231231.xsd#gct_PreferredStockOneAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_0a9ff259-7d14-4d97-beb0-98d0314b56fd" xlink:to="loc_gct_PreferredStockOneAxis_c0c3161d-bfda-4264-9080-6ce7a5dc544a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PreferredStockOneDomain_c0c3161d-bfda-4264-9080-6ce7a5dc544a_default" xlink:href="gct-20231231.xsd#gct_PreferredStockOneDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_gct_PreferredStockOneAxis_c0c3161d-bfda-4264-9080-6ce7a5dc544a" xlink:to="loc_gct_PreferredStockOneDomain_c0c3161d-bfda-4264-9080-6ce7a5dc544a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PreferredStockOneDomain_7c3f3c72-8421-4d8f-a888-9f88a4e3de7e" xlink:href="gct-20231231.xsd#gct_PreferredStockOneDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_gct_PreferredStockOneAxis_c0c3161d-bfda-4264-9080-6ce7a5dc544a" xlink:to="loc_gct_PreferredStockOneDomain_7c3f3c72-8421-4d8f-a888-9f88a4e3de7e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesEPreferredStockMember_04c880c2-7abb-4299-b231-82deb70b3a12" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SeriesEPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_PreferredStockOneDomain_7c3f3c72-8421-4d8f-a888-9f88a4e3de7e" xlink:to="loc_us-gaap_SeriesEPreferredStockMember_04c880c2-7abb-4299-b231-82deb70b3a12" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_InvestorAxis_0bd373f1-fad5-48a6-817c-86dd6ae9a46a" xlink:href="gct-20231231.xsd#gct_InvestorAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_0a9ff259-7d14-4d97-beb0-98d0314b56fd" xlink:to="loc_gct_InvestorAxis_0bd373f1-fad5-48a6-817c-86dd6ae9a46a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_InvestorDomain_0bd373f1-fad5-48a6-817c-86dd6ae9a46a_default" xlink:href="gct-20231231.xsd#gct_InvestorDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_gct_InvestorAxis_0bd373f1-fad5-48a6-817c-86dd6ae9a46a" xlink:to="loc_gct_InvestorDomain_0bd373f1-fad5-48a6-817c-86dd6ae9a46a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_InvestorDomain_287e58cf-b74d-4e27-8c87-f929b7d99801" xlink:href="gct-20231231.xsd#gct_InvestorDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_gct_InvestorAxis_0bd373f1-fad5-48a6-817c-86dd6ae9a46a" xlink:to="loc_gct_InvestorDomain_287e58cf-b74d-4e27-8c87-f929b7d99801" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_HoneySuckleCreekLimitedMember_b5d7d558-4ecd-4ed0-8141-0d873c7fb16e" xlink:href="gct-20231231.xsd#gct_HoneySuckleCreekLimitedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_InvestorDomain_287e58cf-b74d-4e27-8c87-f929b7d99801" xlink:to="loc_gct_HoneySuckleCreekLimitedMember_b5d7d558-4ecd-4ed0-8141-0d873c7fb16e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_HuayYuanInternationalLimitedMember_f01d4eb0-68ee-4016-8377-77f8e77684d0" xlink:href="gct-20231231.xsd#gct_HuayYuanInternationalLimitedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_InvestorDomain_287e58cf-b74d-4e27-8c87-f929b7d99801" xlink:to="loc_gct_HuayYuanInternationalLimitedMember_f01d4eb0-68ee-4016-8377-77f8e77684d0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_HoneySuckleCreekLimitedAndHuayYuanInternationalLimitedMember_0a6b80ee-51f4-4409-adbe-cc8603eb6844" xlink:href="gct-20231231.xsd#gct_HoneySuckleCreekLimitedAndHuayYuanInternationalLimitedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_InvestorDomain_287e58cf-b74d-4e27-8c87-f929b7d99801" xlink:to="loc_gct_HoneySuckleCreekLimitedAndHuayYuanInternationalLimitedMember_0a6b80ee-51f4-4409-adbe-cc8603eb6844" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_c9147399-332c-4c28-842b-5ec4e9764939" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_0a9ff259-7d14-4d97-beb0-98d0314b56fd" xlink:to="loc_us-gaap_StatementClassOfStockAxis_c9147399-332c-4c28-842b-5ec4e9764939" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_c9147399-332c-4c28-842b-5ec4e9764939_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_c9147399-332c-4c28-842b-5ec4e9764939" xlink:to="loc_us-gaap_ClassOfStockDomain_c9147399-332c-4c28-842b-5ec4e9764939_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_0be87008-9bf8-49d1-8b9a-72e5e5a31166" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_c9147399-332c-4c28-842b-5ec4e9764939" xlink:to="loc_us-gaap_ClassOfStockDomain_0be87008-9bf8-49d1-8b9a-72e5e5a31166" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableConvertiblePreferredStockMember_58f50ef5-14bd-4ef4-a691-45b1f47ecf51" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RedeemableConvertiblePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_0be87008-9bf8-49d1-8b9a-72e5e5a31166" xlink:to="loc_us-gaap_RedeemableConvertiblePreferredStockMember_58f50ef5-14bd-4ef4-a691-45b1f47ecf51" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_TemporaryEquityStockSharesIssuedDuringThePeriodShares_766b5a6e-eb00-4df4-aae6-474d0e5f29df" xlink:href="gct-20231231.xsd#gct_TemporaryEquityStockSharesIssuedDuringThePeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_b73d62d3-eb76-40b5-b114-60477dc1dd38" xlink:to="loc_gct_TemporaryEquityStockSharesIssuedDuringThePeriodShares_766b5a6e-eb00-4df4-aae6-474d0e5f29df" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_TemporaryEquitySharesIssuedPricePerShare_e73665cd-0f87-4761-a8d5-6427b42eabe6" xlink:href="gct-20231231.xsd#gct_TemporaryEquitySharesIssuedPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_b73d62d3-eb76-40b5-b114-60477dc1dd38" xlink:to="loc_gct_TemporaryEquitySharesIssuedPricePerShare_e73665cd-0f87-4761-a8d5-6427b42eabe6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfRedeemableConvertiblePreferredStock_70f1e328-be61-4497-81ba-d0a2321500f8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromIssuanceOfRedeemableConvertiblePreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_b73d62d3-eb76-40b5-b114-60477dc1dd38" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfRedeemableConvertiblePreferredStock_70f1e328-be61-4497-81ba-d0a2321500f8" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/PreferredSharesNarrativeRemainingDetails" xlink:type="simple" xlink:href="gct-20231231.xsd#PreferredSharesNarrativeRemainingDetails"/>
  <link:definitionLink xlink:role="http://gig.com/role/PreferredSharesNarrativeRemainingDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityLineItems_a775ea39-995a-4fbf-a4af-5c3e6ef06506" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityByClassOfStockTable_44a89dda-ec19-47cc-9283-f30f74b0bbe5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquityByClassOfStockTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_TemporaryEquityLineItems_a775ea39-995a-4fbf-a4af-5c3e6ef06506" xlink:to="loc_us-gaap_TemporaryEquityByClassOfStockTable_44a89dda-ec19-47cc-9283-f30f74b0bbe5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PreferredStockOneAxis_e08482f1-ce6a-4df3-aa4a-3f71a5b96630" xlink:href="gct-20231231.xsd#gct_PreferredStockOneAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_44a89dda-ec19-47cc-9283-f30f74b0bbe5" xlink:to="loc_gct_PreferredStockOneAxis_e08482f1-ce6a-4df3-aa4a-3f71a5b96630" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PreferredStockOneDomain_e08482f1-ce6a-4df3-aa4a-3f71a5b96630_default" xlink:href="gct-20231231.xsd#gct_PreferredStockOneDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_gct_PreferredStockOneAxis_e08482f1-ce6a-4df3-aa4a-3f71a5b96630" xlink:to="loc_gct_PreferredStockOneDomain_e08482f1-ce6a-4df3-aa4a-3f71a5b96630_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PreferredStockOneDomain_4c5df11e-ad5c-4625-bda9-e4b6714b2345" xlink:href="gct-20231231.xsd#gct_PreferredStockOneDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_gct_PreferredStockOneAxis_e08482f1-ce6a-4df3-aa4a-3f71a5b96630" xlink:to="loc_gct_PreferredStockOneDomain_4c5df11e-ad5c-4625-bda9-e4b6714b2345" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesBPreferredStockMember_f88017c6-1a15-4448-9958-0cd7be870474" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SeriesBPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_PreferredStockOneDomain_4c5df11e-ad5c-4625-bda9-e4b6714b2345" xlink:to="loc_us-gaap_SeriesBPreferredStockMember_f88017c6-1a15-4448-9958-0cd7be870474" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesCPreferredStockMember_9c753f64-48ca-4ee1-a256-f511f834d7d3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SeriesCPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_PreferredStockOneDomain_4c5df11e-ad5c-4625-bda9-e4b6714b2345" xlink:to="loc_us-gaap_SeriesCPreferredStockMember_9c753f64-48ca-4ee1-a256-f511f834d7d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesAPreferredStockMember_2799b577-94ca-430e-9475-e9d611ac8453" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SeriesAPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_PreferredStockOneDomain_4c5df11e-ad5c-4625-bda9-e4b6714b2345" xlink:to="loc_us-gaap_SeriesAPreferredStockMember_2799b577-94ca-430e-9475-e9d611ac8453" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesDPreferredStockMember_b6582b49-26cc-49ba-af6b-f00b881e11df" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SeriesDPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_PreferredStockOneDomain_4c5df11e-ad5c-4625-bda9-e4b6714b2345" xlink:to="loc_us-gaap_SeriesDPreferredStockMember_b6582b49-26cc-49ba-af6b-f00b881e11df" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesEPreferredStockMember_c0d6099b-e548-4819-8e69-3f1aca489b05" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SeriesEPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_PreferredStockOneDomain_4c5df11e-ad5c-4625-bda9-e4b6714b2345" xlink:to="loc_us-gaap_SeriesEPreferredStockMember_c0d6099b-e548-4819-8e69-3f1aca489b05" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OptionIndexedToIssuersEquityTypeAxis_08f340e2-884b-4b7b-bbef-5adaa158b5e5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OptionIndexedToIssuersEquityTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_44a89dda-ec19-47cc-9283-f30f74b0bbe5" xlink:to="loc_us-gaap_OptionIndexedToIssuersEquityTypeAxis_08f340e2-884b-4b7b-bbef-5adaa158b5e5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OptionIndexedToIssuersEquityTypeDomain_08f340e2-884b-4b7b-bbef-5adaa158b5e5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OptionIndexedToIssuersEquityTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityTypeAxis_08f340e2-884b-4b7b-bbef-5adaa158b5e5" xlink:to="loc_us-gaap_OptionIndexedToIssuersEquityTypeDomain_08f340e2-884b-4b7b-bbef-5adaa158b5e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OptionIndexedToIssuersEquityTypeDomain_c3ddc078-c0a7-4254-abe4-d9422049e2a5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OptionIndexedToIssuersEquityTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityTypeAxis_08f340e2-884b-4b7b-bbef-5adaa158b5e5" xlink:to="loc_us-gaap_OptionIndexedToIssuersEquityTypeDomain_c3ddc078-c0a7-4254-abe4-d9422049e2a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_DragAlongRightsMember_55958f1e-dd4c-4a62-8917-50feae8f1cd1" xlink:href="gct-20231231.xsd#gct_DragAlongRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityTypeDomain_c3ddc078-c0a7-4254-abe4-d9422049e2a5" xlink:to="loc_gct_DragAlongRightsMember_55958f1e-dd4c-4a62-8917-50feae8f1cd1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_e2aacd17-6bee-4eed-bc8b-226979fc997a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_44a89dda-ec19-47cc-9283-f30f74b0bbe5" xlink:to="loc_us-gaap_StatementClassOfStockAxis_e2aacd17-6bee-4eed-bc8b-226979fc997a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_e2aacd17-6bee-4eed-bc8b-226979fc997a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_e2aacd17-6bee-4eed-bc8b-226979fc997a" xlink:to="loc_us-gaap_ClassOfStockDomain_e2aacd17-6bee-4eed-bc8b-226979fc997a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_c514fbf2-30cd-43cf-b419-7028a9896a45" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_e2aacd17-6bee-4eed-bc8b-226979fc997a" xlink:to="loc_us-gaap_ClassOfStockDomain_c514fbf2-30cd-43cf-b419-7028a9896a45" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonredeemableConvertiblePreferredStockMember_105af7db-48ee-44f3-8929-267e238a5ee0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NonredeemableConvertiblePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_c514fbf2-30cd-43cf-b419-7028a9896a45" xlink:to="loc_us-gaap_NonredeemableConvertiblePreferredStockMember_105af7db-48ee-44f3-8929-267e238a5ee0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableConvertiblePreferredStockMember_b13044e6-1e0a-467f-b0b6-358884710590" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RedeemableConvertiblePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_c514fbf2-30cd-43cf-b419-7028a9896a45" xlink:to="loc_us-gaap_RedeemableConvertiblePreferredStockMember_b13044e6-1e0a-467f-b0b6-358884710590" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_0a30e6c4-888f-463b-926d-5d420daeb751" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_44a89dda-ec19-47cc-9283-f30f74b0bbe5" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_0a30e6c4-888f-463b-926d-5d420daeb751" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_0a30e6c4-888f-463b-926d-5d420daeb751_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_0a30e6c4-888f-463b-926d-5d420daeb751" xlink:to="loc_us-gaap_EquityComponentDomain_0a30e6c4-888f-463b-926d-5d420daeb751_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_ddabb9c6-dd79-4c96-88b6-404f6ac2634a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_0a30e6c4-888f-463b-926d-5d420daeb751" xlink:to="loc_us-gaap_EquityComponentDomain_ddabb9c6-dd79-4c96-88b6-404f6ac2634a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_30793c74-e497-4b76-afc0-e54de7b99bb9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_ddabb9c6-dd79-4c96-88b6-404f6ac2634a" xlink:to="loc_us-gaap_CommonStockMember_30793c74-e497-4b76-afc0-e54de7b99bb9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ProspectiveEventAxis_e4096983-08b5-4a6b-8442-81b6c8766770" xlink:href="gct-20231231.xsd#gct_ProspectiveEventAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_44a89dda-ec19-47cc-9283-f30f74b0bbe5" xlink:to="loc_gct_ProspectiveEventAxis_e4096983-08b5-4a6b-8442-81b6c8766770" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ProspectiveEventDomain_e4096983-08b5-4a6b-8442-81b6c8766770_default" xlink:href="gct-20231231.xsd#gct_ProspectiveEventDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_gct_ProspectiveEventAxis_e4096983-08b5-4a6b-8442-81b6c8766770" xlink:to="loc_gct_ProspectiveEventDomain_e4096983-08b5-4a6b-8442-81b6c8766770_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ProspectiveEventDomain_86773b6a-f7fa-4c8c-8247-5cc1a56eb8ad" xlink:href="gct-20231231.xsd#gct_ProspectiveEventDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_gct_ProspectiveEventAxis_e4096983-08b5-4a6b-8442-81b6c8766770" xlink:to="loc_gct_ProspectiveEventDomain_86773b6a-f7fa-4c8c-8247-5cc1a56eb8ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_TriggeringOfRightsBeforeTheFifthAnniversaryMember_2cbc7b7b-2351-4e93-a721-3938d1de8371" xlink:href="gct-20231231.xsd#gct_TriggeringOfRightsBeforeTheFifthAnniversaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ProspectiveEventDomain_86773b6a-f7fa-4c8c-8247-5cc1a56eb8ad" xlink:to="loc_gct_TriggeringOfRightsBeforeTheFifthAnniversaryMember_2cbc7b7b-2351-4e93-a721-3938d1de8371" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_TimeToCompleteAQualifiedIPO_9db85688-7cc9-43d5-8f4c-bdc11dc5cba0" xlink:href="gct-20231231.xsd#gct_TimeToCompleteAQualifiedIPO"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_a775ea39-995a-4fbf-a4af-5c3e6ef06506" xlink:to="loc_gct_TimeToCompleteAQualifiedIPO_9db85688-7cc9-43d5-8f4c-bdc11dc5cba0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_TemporaryEquityRedemptionPricePercentage_28bd0b2a-353d-486c-8858-2a52dc0e378f" xlink:href="gct-20231231.xsd#gct_TemporaryEquityRedemptionPricePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_a775ea39-995a-4fbf-a4af-5c3e6ef06506" xlink:to="loc_gct_TemporaryEquityRedemptionPricePercentage_28bd0b2a-353d-486c-8858-2a52dc0e378f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_TemporaryEquityInterestRatePercentageOnRedemptionPrice_7038c134-4a21-4825-bc20-7add25729ad1" xlink:href="gct-20231231.xsd#gct_TemporaryEquityInterestRatePercentageOnRedemptionPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_a775ea39-995a-4fbf-a4af-5c3e6ef06506" xlink:to="loc_gct_TemporaryEquityInterestRatePercentageOnRedemptionPrice_7038c134-4a21-4825-bc20-7add25729ad1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockConvertibleConversionRatio_3ea6167d-90bf-40eb-a650-86381009c9e5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PreferredStockConvertibleConversionRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_a775ea39-995a-4fbf-a4af-5c3e6ef06506" xlink:to="loc_us-gaap_PreferredStockConvertibleConversionRatio_3ea6167d-90bf-40eb-a650-86381009c9e5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PercentageOfVotesInTermOfValueRequiredForConversionIntoCommonStock_9ffbfd46-5ba1-4552-a3cd-a822774716de" xlink:href="gct-20231231.xsd#gct_PercentageOfVotesInTermOfValueRequiredForConversionIntoCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_a775ea39-995a-4fbf-a4af-5c3e6ef06506" xlink:to="loc_gct_PercentageOfVotesInTermOfValueRequiredForConversionIntoCommonStock_9ffbfd46-5ba1-4552-a3cd-a822774716de" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockDividendRatePercentage_2dc4da32-88d5-441a-97fc-207ce93c8c7e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PreferredStockDividendRatePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_a775ea39-995a-4fbf-a4af-5c3e6ef06506" xlink:to="loc_us-gaap_PreferredStockDividendRatePercentage_2dc4da32-88d5-441a-97fc-207ce93c8c7e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PreferredStockLiquidationPreferencePercentage_18fdb9a5-2492-4f5c-9d79-8933b3ce67a9" xlink:href="gct-20231231.xsd#gct_PreferredStockLiquidationPreferencePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_a775ea39-995a-4fbf-a4af-5c3e6ef06506" xlink:to="loc_gct_PreferredStockLiquidationPreferencePercentage_18fdb9a5-2492-4f5c-9d79-8933b3ce67a9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_TemporaryEquityLiquidationPreferencePercentage_51dcc02a-b708-46db-b16d-a7a1a957b89c" xlink:href="gct-20231231.xsd#gct_TemporaryEquityLiquidationPreferencePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_a775ea39-995a-4fbf-a4af-5c3e6ef06506" xlink:to="loc_gct_TemporaryEquityLiquidationPreferencePercentage_51dcc02a-b708-46db-b16d-a7a1a957b89c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PercentageOfVotesInTermsOfValueRequiredForAShareholderToPurchaseSharesFromOtherShareholders_d03c3de7-a96f-4d70-be65-970bda480255" xlink:href="gct-20231231.xsd#gct_PercentageOfVotesInTermsOfValueRequiredForAShareholderToPurchaseSharesFromOtherShareholders"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_a775ea39-995a-4fbf-a4af-5c3e6ef06506" xlink:to="loc_gct_PercentageOfVotesInTermsOfValueRequiredForAShareholderToPurchaseSharesFromOtherShareholders_d03c3de7-a96f-4d70-be65-970bda480255" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_NumberOfDaysOfNoticeToBeGivenToShareholdersByTheCompanyForSharePurchase_c74a4a9a-f27a-4b53-a893-99a706e0e9b0" xlink:href="gct-20231231.xsd#gct_NumberOfDaysOfNoticeToBeGivenToShareholdersByTheCompanyForSharePurchase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_a775ea39-995a-4fbf-a4af-5c3e6ef06506" xlink:to="loc_gct_NumberOfDaysOfNoticeToBeGivenToShareholdersByTheCompanyForSharePurchase_c74a4a9a-f27a-4b53-a893-99a706e0e9b0" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_EstimatedMinimumProceedsFromPreferredStock_78f07a72-e93a-41e4-a77f-a68a8cb9b4cc" xlink:href="gct-20231231.xsd#gct_EstimatedMinimumProceedsFromPreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_a775ea39-995a-4fbf-a4af-5c3e6ef06506" xlink:to="loc_gct_EstimatedMinimumProceedsFromPreferredStock_78f07a72-e93a-41e4-a77f-a68a8cb9b4cc" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/PreferredSharesScheduleofTemporaryEquityDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#PreferredSharesScheduleofTemporaryEquityDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/PreferredSharesScheduleofTemporaryEquityDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityLineItems_25e5dad1-a984-4344-adf8-d371c9c1fc96" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityByClassOfStockTable_b6306039-c3c2-4cf8-90f5-017576811f67" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquityByClassOfStockTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_TemporaryEquityLineItems_25e5dad1-a984-4344-adf8-d371c9c1fc96" xlink:to="loc_us-gaap_TemporaryEquityByClassOfStockTable_b6306039-c3c2-4cf8-90f5-017576811f67" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PreferredStockOneAxis_b4aafa90-7f47-452a-b435-f637f5bc4534" xlink:href="gct-20231231.xsd#gct_PreferredStockOneAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_b6306039-c3c2-4cf8-90f5-017576811f67" xlink:to="loc_gct_PreferredStockOneAxis_b4aafa90-7f47-452a-b435-f637f5bc4534" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PreferredStockOneDomain_b4aafa90-7f47-452a-b435-f637f5bc4534_default" xlink:href="gct-20231231.xsd#gct_PreferredStockOneDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_gct_PreferredStockOneAxis_b4aafa90-7f47-452a-b435-f637f5bc4534" xlink:to="loc_gct_PreferredStockOneDomain_b4aafa90-7f47-452a-b435-f637f5bc4534_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PreferredStockOneDomain_70fdfc44-59e7-4fdd-a886-d80abaabe6e1" xlink:href="gct-20231231.xsd#gct_PreferredStockOneDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_gct_PreferredStockOneAxis_b4aafa90-7f47-452a-b435-f637f5bc4534" xlink:to="loc_gct_PreferredStockOneDomain_70fdfc44-59e7-4fdd-a886-d80abaabe6e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesEPreferredStockMember_6ccf7048-5f5d-4f8c-80e4-ba19dfa4a6ba" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SeriesEPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_PreferredStockOneDomain_70fdfc44-59e7-4fdd-a886-d80abaabe6e1" xlink:to="loc_us-gaap_SeriesEPreferredStockMember_6ccf7048-5f5d-4f8c-80e4-ba19dfa4a6ba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_f248eb61-fa87-44df-965a-759a618c881c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_b6306039-c3c2-4cf8-90f5-017576811f67" xlink:to="loc_us-gaap_StatementClassOfStockAxis_f248eb61-fa87-44df-965a-759a618c881c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_f248eb61-fa87-44df-965a-759a618c881c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_f248eb61-fa87-44df-965a-759a618c881c" xlink:to="loc_us-gaap_ClassOfStockDomain_f248eb61-fa87-44df-965a-759a618c881c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_7243a76e-e3e2-4999-9d0d-0865c0aac3df" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_f248eb61-fa87-44df-965a-759a618c881c" xlink:to="loc_us-gaap_ClassOfStockDomain_7243a76e-e3e2-4999-9d0d-0865c0aac3df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableConvertiblePreferredStockMember_fb5b0f5c-3a62-45c8-be4b-24f7f110cbfc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RedeemableConvertiblePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_7243a76e-e3e2-4999-9d0d-0865c0aac3df" xlink:to="loc_us-gaap_RedeemableConvertiblePreferredStockMember_fb5b0f5c-3a62-45c8-be4b-24f7f110cbfc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestEquityPreferredCarryingAmount_2d2eb950-553e-42f6-b849-c1c9f79be15e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RedeemableNoncontrollingInterestEquityPreferredCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_25e5dad1-a984-4344-adf8-d371c9c1fc96" xlink:to="loc_us-gaap_RedeemableNoncontrollingInterestEquityPreferredCarryingAmount_2d2eb950-553e-42f6-b849-c1c9f79be15e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityAccretionToRedemptionValue_9134a878-6d4d-421c-9a8c-8994a97369d2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquityAccretionToRedemptionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_25e5dad1-a984-4344-adf8-d371c9c1fc96" xlink:to="loc_us-gaap_TemporaryEquityAccretionToRedemptionValue_9134a878-6d4d-421c-9a8c-8994a97369d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfUnits_61974628-9885-45c3-833c-68f7be6da18d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodValueConversionOfUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_25e5dad1-a984-4344-adf8-d371c9c1fc96" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfUnits_61974628-9885-45c3-833c-68f7be6da18d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestEquityPreferredCarryingAmount_d45faf42-4345-4b89-913b-70ca5ca0dec5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RedeemableNoncontrollingInterestEquityPreferredCarryingAmount"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/OrdinarySharesAdditionalInformationDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#OrdinarySharesAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/OrdinarySharesAdditionalInformationDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_7993bb59-c431-4bb2-8093-b49d3c9a2be1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_StatementTable_7993bb59-c431-4bb2-8093-b49d3c9a2be1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_efe36726-94bb-4d4d-9870-aa0c4e7148c7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_7993bb59-c431-4bb2-8093-b49d3c9a2be1" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_efe36726-94bb-4d4d-9870-aa0c4e7148c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_efe36726-94bb-4d4d-9870-aa0c4e7148c7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_efe36726-94bb-4d4d-9870-aa0c4e7148c7" xlink:to="loc_us-gaap_EquityComponentDomain_efe36726-94bb-4d4d-9870-aa0c4e7148c7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_dcac792d-4f61-40a1-a77c-96a2e6201684" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_efe36726-94bb-4d4d-9870-aa0c4e7148c7" xlink:to="loc_us-gaap_EquityComponentDomain_dcac792d-4f61-40a1-a77c-96a2e6201684" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_3474245c-6e55-479c-8bc7-3722d8887886" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_dcac792d-4f61-40a1-a77c-96a2e6201684" xlink:to="loc_us-gaap_CommonStockMember_3474245c-6e55-479c-8bc7-3722d8887886" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_5f929cf1-3323-4830-bb4f-74497c94172d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_7993bb59-c431-4bb2-8093-b49d3c9a2be1" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_5f929cf1-3323-4830-bb4f-74497c94172d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_5f929cf1-3323-4830-bb4f-74497c94172d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_5f929cf1-3323-4830-bb4f-74497c94172d" xlink:to="loc_us-gaap_RelatedPartyDomain_5f929cf1-3323-4830-bb4f-74497c94172d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_d7d7cfe4-03e7-4300-b8ab-839761a8845a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_5f929cf1-3323-4830-bb4f-74497c94172d" xlink:to="loc_us-gaap_RelatedPartyDomain_d7d7cfe4-03e7-4300-b8ab-839761a8845a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_TrustHoldcosMember_cf3d8049-b007-4740-a5e7-2208e980b477" xlink:href="gct-20231231.xsd#gct_TrustHoldcosMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_d7d7cfe4-03e7-4300-b8ab-839761a8845a" xlink:to="loc_gct_TrustHoldcosMember_cf3d8049-b007-4740-a5e7-2208e980b477" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_Mr.larryLeiWuMember_4d131759-dfd8-48d2-b714-a14d74c8a17c" xlink:href="gct-20231231.xsd#gct_Mr.larryLeiWuMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_d7d7cfe4-03e7-4300-b8ab-839761a8845a" xlink:to="loc_gct_Mr.larryLeiWuMember_4d131759-dfd8-48d2-b714-a14d74c8a17c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_OtherShareholdersMember_3cad1915-ca38-44dc-a43b-08796a269d6c" xlink:href="gct-20231231.xsd#gct_OtherShareholdersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_d7d7cfe4-03e7-4300-b8ab-839761a8845a" xlink:to="loc_gct_OtherShareholdersMember_3cad1915-ca38-44dc-a43b-08796a269d6c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_230d0002-3419-48d4-a784-4302af78a77f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConversionOfStockByUniqueDescriptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_7993bb59-c431-4bb2-8093-b49d3c9a2be1" xlink:to="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_230d0002-3419-48d4-a784-4302af78a77f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_230d0002-3419-48d4-a784-4302af78a77f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConversionOfStockNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_230d0002-3419-48d4-a784-4302af78a77f" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_230d0002-3419-48d4-a784-4302af78a77f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_cd7b0623-eed5-45f8-83b2-0ae194226b35" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConversionOfStockNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_230d0002-3419-48d4-a784-4302af78a77f" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_cd7b0623-eed5-45f8-83b2-0ae194226b35" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ConversionOfSeriesBRedeemableConvertiblePreferredSharesToClassbOrdinarySharesMember_748f8f6a-fd74-4f27-a00b-ff76b9e46183" xlink:href="gct-20231231.xsd#gct_ConversionOfSeriesBRedeemableConvertiblePreferredSharesToClassbOrdinarySharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_cd7b0623-eed5-45f8-83b2-0ae194226b35" xlink:to="loc_gct_ConversionOfSeriesBRedeemableConvertiblePreferredSharesToClassbOrdinarySharesMember_748f8f6a-fd74-4f27-a00b-ff76b9e46183" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ConversionOfTemporaryEquitySeriesEPreferredSharesToClassAOrdinarySharesMember_77302c57-9f3f-423f-bada-b9b546191281" xlink:href="gct-20231231.xsd#gct_ConversionOfTemporaryEquitySeriesEPreferredSharesToClassAOrdinarySharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_cd7b0623-eed5-45f8-83b2-0ae194226b35" xlink:to="loc_gct_ConversionOfTemporaryEquitySeriesEPreferredSharesToClassAOrdinarySharesMember_77302c57-9f3f-423f-bada-b9b546191281" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ConversionOfPreferredSharesToClassAOrdinarySharesMember_45a23f17-aac4-4cd1-a365-44e56776de24" xlink:href="gct-20231231.xsd#gct_ConversionOfPreferredSharesToClassAOrdinarySharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_cd7b0623-eed5-45f8-83b2-0ae194226b35" xlink:to="loc_gct_ConversionOfPreferredSharesToClassAOrdinarySharesMember_45a23f17-aac4-4cd1-a365-44e56776de24" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_67455faf-f899-4504-8ea1-d13021de4534" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_7993bb59-c431-4bb2-8093-b49d3c9a2be1" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_67455faf-f899-4504-8ea1-d13021de4534" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_67455faf-f899-4504-8ea1-d13021de4534_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_67455faf-f899-4504-8ea1-d13021de4534" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_67455faf-f899-4504-8ea1-d13021de4534_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_5adf87ec-5006-4416-944e-41638f5a5ce1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_67455faf-f899-4504-8ea1-d13021de4534" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_5adf87ec-5006-4416-944e-41638f5a5ce1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_31f7fac5-d1c2-47b0-a136-d76c7f8eb922" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_5adf87ec-5006-4416-944e-41638f5a5ce1" xlink:to="loc_us-gaap_CommonClassAMember_31f7fac5-d1c2-47b0-a136-d76c7f8eb922" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_9b558040-c064-494d-8b3e-2dee16ac39ae" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_5adf87ec-5006-4416-944e-41638f5a5ce1" xlink:to="loc_us-gaap_CommonClassBMember_9b558040-c064-494d-8b3e-2dee16ac39ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IPOMember_1a8464a3-5361-4ff9-96ea-6942be96646d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IPOMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_5adf87ec-5006-4416-944e-41638f5a5ce1" xlink:to="loc_us-gaap_IPOMember_1a8464a3-5361-4ff9-96ea-6942be96646d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OverAllotmentOptionMember_813706af-a293-4116-aec0-0c0c3e9e1c1f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OverAllotmentOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_5adf87ec-5006-4416-944e-41638f5a5ce1" xlink:to="loc_us-gaap_OverAllotmentOptionMember_813706af-a293-4116-aec0-0c0c3e9e1c1f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_f6c0b0cc-c460-4a7a-9285-0ebc92a2489a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_7993bb59-c431-4bb2-8093-b49d3c9a2be1" xlink:to="loc_us-gaap_AwardTypeAxis_f6c0b0cc-c460-4a7a-9285-0ebc92a2489a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f6c0b0cc-c460-4a7a-9285-0ebc92a2489a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_f6c0b0cc-c460-4a7a-9285-0ebc92a2489a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f6c0b0cc-c460-4a7a-9285-0ebc92a2489a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_30a1eb7e-7dee-47bb-8440-c954f856bfcb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_f6c0b0cc-c460-4a7a-9285-0ebc92a2489a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_30a1eb7e-7dee-47bb-8440-c954f856bfcb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_eaa65c80-b827-4699-b1c2-1021e941e276" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_30a1eb7e-7dee-47bb-8440-c954f856bfcb" xlink:to="loc_us-gaap_RestrictedStockMember_eaa65c80-b827-4699-b1c2-1021e941e276" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_GranteeServicePeriodAxis_05379ad4-3494-4bb9-b330-296256ad0f0f" xlink:href="gct-20231231.xsd#gct_GranteeServicePeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_7993bb59-c431-4bb2-8093-b49d3c9a2be1" xlink:to="loc_gct_GranteeServicePeriodAxis_05379ad4-3494-4bb9-b330-296256ad0f0f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_GranteeServicePeriodDomain_05379ad4-3494-4bb9-b330-296256ad0f0f_default" xlink:href="gct-20231231.xsd#gct_GranteeServicePeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_gct_GranteeServicePeriodAxis_05379ad4-3494-4bb9-b330-296256ad0f0f" xlink:to="loc_gct_GranteeServicePeriodDomain_05379ad4-3494-4bb9-b330-296256ad0f0f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_GranteeServicePeriodDomain_f033d851-d850-49a7-a3a0-1a12632ed142" xlink:href="gct-20231231.xsd#gct_GranteeServicePeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_gct_GranteeServicePeriodAxis_05379ad4-3494-4bb9-b330-296256ad0f0f" xlink:to="loc_gct_GranteeServicePeriodDomain_f033d851-d850-49a7-a3a0-1a12632ed142" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ThreeYearMember_72ac485a-efe3-4f9b-8b97-f23d7bfa2643" xlink:href="gct-20231231.xsd#gct_ThreeYearMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_GranteeServicePeriodDomain_f033d851-d850-49a7-a3a0-1a12632ed142" xlink:to="loc_gct_ThreeYearMember_72ac485a-efe3-4f9b-8b97-f23d7bfa2643" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_0ff59070-f04f-40b4-b709-c1dd1a1b2622" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_7993bb59-c431-4bb2-8093-b49d3c9a2be1" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_0ff59070-f04f-40b4-b709-c1dd1a1b2622" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_0ff59070-f04f-40b4-b709-c1dd1a1b2622_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_0ff59070-f04f-40b4-b709-c1dd1a1b2622" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_0ff59070-f04f-40b4-b709-c1dd1a1b2622_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_c1ec8cca-2fa3-4bce-96c4-9f7b84eb4ba7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_0ff59070-f04f-40b4-b709-c1dd1a1b2622" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_c1ec8cca-2fa3-4bce-96c4-9f7b84eb4ba7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_0d0a0ad8-2ab9-448a-be31-3b32cc8bc645" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_c1ec8cca-2fa3-4bce-96c4-9f7b84eb4ba7" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_0d0a0ad8-2ab9-448a-be31-3b32cc8bc645" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_e079ca75-f68d-4436-b050-ddd982a0e39f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_7993bb59-c431-4bb2-8093-b49d3c9a2be1" xlink:to="loc_us-gaap_StatementClassOfStockAxis_e079ca75-f68d-4436-b050-ddd982a0e39f" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_e079ca75-f68d-4436-b050-ddd982a0e39f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_e079ca75-f68d-4436-b050-ddd982a0e39f" xlink:to="loc_us-gaap_ClassOfStockDomain_e079ca75-f68d-4436-b050-ddd982a0e39f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_15b7c6d9-60e0-4dec-a6a4-c1f9ec42605a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_e079ca75-f68d-4436-b050-ddd982a0e39f" xlink:to="loc_us-gaap_ClassOfStockDomain_15b7c6d9-60e0-4dec-a6a4-c1f9ec42605a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_a4294c03-7f04-40d8-8013-42e482997e42" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_15b7c6d9-60e0-4dec-a6a4-c1f9ec42605a" xlink:to="loc_us-gaap_CommonClassAMember_a4294c03-7f04-40d8-8013-42e482997e42" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_e9204a40-8401-4e32-a076-6902ddd9ac56" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_e9204a40-8401-4e32-a076-6902ddd9ac56" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_0feaf8a2-6483-4ef8-a018-bd08b9c5152c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_CommonStockSharesIssued_0feaf8a2-6483-4ef8-a018-bd08b9c5152c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_5a67b0a8-ba6f-456c-89bb-68d216c0b66e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_5a67b0a8-ba6f-456c-89bb-68d216c0b66e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_83c15896-01f6-4ad8-8e5e-7f315bf8ec51" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_83c15896-01f6-4ad8-8e5e-7f315bf8ec51" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesIssuedForServices_9d4b8569-28cb-4948-ae89-7b29371ca3dd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesIssuedForServices"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesIssuedForServices_9d4b8569-28cb-4948-ae89-7b29371ca3dd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueIssuedForServices_7258196c-f153-4d16-b504-a77e7e49a07b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodValueIssuedForServices"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueIssuedForServices_7258196c-f153-4d16-b504-a77e7e49a07b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_d780e4be-7cf6-4252-bb67-b98221f76b6a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_d780e4be-7cf6-4252-bb67-b98221f76b6a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesHeldInEmployeeTrustShares_d1769314-2bbe-4d69-a3b6-2ed6a8fae2ef" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesHeldInEmployeeTrustShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_CommonStockSharesHeldInEmployeeTrustShares_d1769314-2bbe-4d69-a3b6-2ed6a8fae2ef" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_c7941e7d-251a-4c74-8b88-90cd1f05ef3b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_c7941e7d-251a-4c74-8b88-90cd1f05ef3b" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_44f1ab7f-9cea-4103-8749-8b136f92584d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_44f1ab7f-9cea-4103-8749-8b136f92584d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_de6b681e-a89b-4b2d-80e9-9e390250504b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_de6b681e-a89b-4b2d-80e9-9e390250504b" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockVotingRights_9dea87b8-2154-4e4f-8085-1b27757f4d79" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockVotingRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_CommonStockVotingRights_9dea87b8-2154-4e4f-8085-1b27757f4d79" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion_7fff5688-c2b7-4b50-8825-4515c170d3bc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion_7fff5688-c2b7-4b50-8825-4515c170d3bc" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockSharesConverted1_05f2fe7d-5297-4327-8ef4-2ceea70cbdcb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConversionOfStockSharesConverted1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_ConversionOfStockSharesConverted1_05f2fe7d-5297-4327-8ef4-2ceea70cbdcb" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockDescription_c234f955-b8b5-419a-b9b4-62bc72d8026a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConversionOfStockDescription"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_ConversionOfStockDescription_c234f955-b8b5-419a-b9b4-62bc72d8026a" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockSharesIssued1_c15e3219-4a2a-40ef-ab09-e22c9224cee9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConversionOfStockSharesIssued1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_ConversionOfStockSharesIssued1_c15e3219-4a2a-40ef-ab09-e22c9224cee9" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_0f646b8b-d7fe-4c57-bcae-f4830a4d0862" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_0f646b8b-d7fe-4c57-bcae-f4830a4d0862" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockPricePerShare_b5140da9-989f-4995-aa05-767b33b0e780" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_SaleOfStockPricePerShare_b5140da9-989f-4995-aa05-767b33b0e780" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_b0bdebef-beaf-40a4-84e7-d3b2e8dd07bf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_b0bdebef-beaf-40a4-84e7-d3b2e8dd07bf" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_UnderwritingCommissionsAndOtherOfferingExpenses_c1489751-3c02-4808-8e25-3b9e93d8dd18" xlink:href="gct-20231231.xsd#gct_UnderwritingCommissionsAndOtherOfferingExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_gct_UnderwritingCommissionsAndOtherOfferingExpenses_c1489751-3c02-4808-8e25-3b9e93d8dd18" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchaseProgramAuthorizedAmount1_d2c91e20-43b2-4203-ab74-5f0f447a9874" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockRepurchaseProgramAuthorizedAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_StockRepurchaseProgramAuthorizedAmount1_d2c91e20-43b2-4203-ab74-5f0f447a9874" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockAcquiredAverageCostPerShare_6f9abb29-d54c-41d7-bf28-7a07b6053a2c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TreasuryStockAcquiredAverageCostPerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_TreasuryStockAcquiredAverageCostPerShare_6f9abb29-d54c-41d7-bf28-7a07b6053a2c" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockSharesAcquired_0ba5b11d-3a25-4dce-b9b8-811da480066e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TreasuryStockSharesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_TreasuryStockSharesAcquired_0ba5b11d-3a25-4dce-b9b8-811da480066e" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_7944c88f-3940-4faa-907e-a6268563bb50" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TreasuryStockValueAcquiredCostMethod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_7944c88f-3940-4faa-907e-a6268563bb50" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentOfFinancingAndStockIssuanceCosts_21c8f5f5-ebb0-437b-8d90-1c7f1c974c74" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentOfFinancingAndStockIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3431de-72ca-4ea9-8b42-65d1e625da59" xlink:to="loc_us-gaap_PaymentOfFinancingAndStockIssuanceCosts_21c8f5f5-ebb0-437b-8d90-1c7f1c974c74" xlink:type="arc" order="24"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/ShareBasedCompensationAdditionalinformationDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#ShareBasedCompensationAdditionalinformationDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/ShareBasedCompensationAdditionalinformationDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e60e5512-ba55-4fce-a4b5-0d1f229c6075" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_589bf1ed-fb96-4689-9edb-96be68e5794d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e60e5512-ba55-4fce-a4b5-0d1f229c6075" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_589bf1ed-fb96-4689-9edb-96be68e5794d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_5deb7b93-6cd6-48a1-901a-1e3d848790e2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_589bf1ed-fb96-4689-9edb-96be68e5794d" xlink:to="loc_us-gaap_PlanNameAxis_5deb7b93-6cd6-48a1-901a-1e3d848790e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_5deb7b93-6cd6-48a1-901a-1e3d848790e2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_5deb7b93-6cd6-48a1-901a-1e3d848790e2" xlink:to="loc_us-gaap_PlanNameDomain_5deb7b93-6cd6-48a1-901a-1e3d848790e2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_278d1d41-58f7-4a2a-8988-b473a3cc4a1c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_5deb7b93-6cd6-48a1-901a-1e3d848790e2" xlink:to="loc_us-gaap_PlanNameDomain_278d1d41-58f7-4a2a-8988-b473a3cc4a1c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_TwoThousandSeventeenShareIncentivePlanMember_e866830b-241b-4cbb-b0d6-affe6d47bca7" xlink:href="gct-20231231.xsd#gct_TwoThousandSeventeenShareIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_278d1d41-58f7-4a2a-8988-b473a3cc4a1c" xlink:to="loc_gct_TwoThousandSeventeenShareIncentivePlanMember_e866830b-241b-4cbb-b0d6-affe6d47bca7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusAxis_d8e6c436-463e-461d-a814-f2598e359a95" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GranteeStatusAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_589bf1ed-fb96-4689-9edb-96be68e5794d" xlink:to="loc_us-gaap_GranteeStatusAxis_d8e6c436-463e-461d-a814-f2598e359a95" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_d8e6c436-463e-461d-a814-f2598e359a95_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GranteeStatusAxis_d8e6c436-463e-461d-a814-f2598e359a95" xlink:to="loc_us-gaap_GranteeStatusDomain_d8e6c436-463e-461d-a814-f2598e359a95_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_0109e8d5-d25c-495c-ac75-89244c48747b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GranteeStatusAxis_d8e6c436-463e-461d-a814-f2598e359a95" xlink:to="loc_us-gaap_GranteeStatusDomain_0109e8d5-d25c-495c-ac75-89244c48747b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedPaymentArrangementNonemployeeMember_cd905e6d-c46e-43de-995c-5ac94b4ed8b2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedPaymentArrangementNonemployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_0109e8d5-d25c-495c-ac75-89244c48747b" xlink:to="loc_us-gaap_ShareBasedPaymentArrangementNonemployeeMember_cd905e6d-c46e-43de-995c-5ac94b4ed8b2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ShareBasedPaymentArrangementDirectorsAndEmployeeMember_730b3b03-cbc8-4d4a-af2c-12f07ced1492" xlink:href="gct-20231231.xsd#gct_ShareBasedPaymentArrangementDirectorsAndEmployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_0109e8d5-d25c-495c-ac75-89244c48747b" xlink:to="loc_gct_ShareBasedPaymentArrangementDirectorsAndEmployeeMember_730b3b03-cbc8-4d4a-af2c-12f07ced1492" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedPaymentArrangementEmployeeMember_4d3466c5-d085-4506-ae53-033c9b916f1b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedPaymentArrangementEmployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_0109e8d5-d25c-495c-ac75-89244c48747b" xlink:to="loc_us-gaap_ShareBasedPaymentArrangementEmployeeMember_4d3466c5-d085-4506-ae53-033c9b916f1b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_GranteeServicePeriodAxis_aac58ebb-5ceb-482b-af49-8c3e305ae29f" xlink:href="gct-20231231.xsd#gct_GranteeServicePeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_589bf1ed-fb96-4689-9edb-96be68e5794d" xlink:to="loc_gct_GranteeServicePeriodAxis_aac58ebb-5ceb-482b-af49-8c3e305ae29f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_GranteeServicePeriodDomain_aac58ebb-5ceb-482b-af49-8c3e305ae29f_default" xlink:href="gct-20231231.xsd#gct_GranteeServicePeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_gct_GranteeServicePeriodAxis_aac58ebb-5ceb-482b-af49-8c3e305ae29f" xlink:to="loc_gct_GranteeServicePeriodDomain_aac58ebb-5ceb-482b-af49-8c3e305ae29f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_GranteeServicePeriodDomain_36e8b65c-3333-464a-b7a4-d959a784a1b8" xlink:href="gct-20231231.xsd#gct_GranteeServicePeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_gct_GranteeServicePeriodAxis_aac58ebb-5ceb-482b-af49-8c3e305ae29f" xlink:to="loc_gct_GranteeServicePeriodDomain_36e8b65c-3333-464a-b7a4-d959a784a1b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ThreeYearMember_c5cd15e9-c7eb-48c0-8dce-6e3416adb0aa" xlink:href="gct-20231231.xsd#gct_ThreeYearMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_GranteeServicePeriodDomain_36e8b65c-3333-464a-b7a4-d959a784a1b8" xlink:to="loc_gct_ThreeYearMember_c5cd15e9-c7eb-48c0-8dce-6e3416adb0aa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_d21e6cbd-4f29-4c7c-94a0-65caaedb2398" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_589bf1ed-fb96-4689-9edb-96be68e5794d" xlink:to="loc_us-gaap_AwardTypeAxis_d21e6cbd-4f29-4c7c-94a0-65caaedb2398" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d21e6cbd-4f29-4c7c-94a0-65caaedb2398_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_d21e6cbd-4f29-4c7c-94a0-65caaedb2398" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d21e6cbd-4f29-4c7c-94a0-65caaedb2398_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_210f152d-9685-473f-82ce-24d64f63b8fe" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_d21e6cbd-4f29-4c7c-94a0-65caaedb2398" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_210f152d-9685-473f-82ce-24d64f63b8fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_473e5e84-835a-4267-8bf9-5a07cbf3b83f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_210f152d-9685-473f-82ce-24d64f63b8fe" xlink:to="loc_us-gaap_EmployeeStockOptionMember_473e5e84-835a-4267-8bf9-5a07cbf3b83f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_04934e94-66fc-4120-8969-f3296481f8ce" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_210f152d-9685-473f-82ce-24d64f63b8fe" xlink:to="loc_us-gaap_RestrictedStockMember_04934e94-66fc-4120-8969-f3296481f8ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_c41a9a15-5c38-4dcb-b875-76c36ddca73d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_210f152d-9685-473f-82ce-24d64f63b8fe" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_c41a9a15-5c38-4dcb-b875-76c36ddca73d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_b9ecc9ac-d53a-4301-8f61-5183b3871682" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_589bf1ed-fb96-4689-9edb-96be68e5794d" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_b9ecc9ac-d53a-4301-8f61-5183b3871682" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_b9ecc9ac-d53a-4301-8f61-5183b3871682_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_b9ecc9ac-d53a-4301-8f61-5183b3871682" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_b9ecc9ac-d53a-4301-8f61-5183b3871682_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_9988a971-6d93-482b-bed5-5a6642f79392" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_b9ecc9ac-d53a-4301-8f61-5183b3871682" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_9988a971-6d93-482b-bed5-5a6642f79392" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_7a2714d1-1e0d-4872-abb5-e65b654b1c80" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_9988a971-6d93-482b-bed5-5a6642f79392" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_7a2714d1-1e0d-4872-abb5-e65b654b1c80" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_638406b9-3913-42b1-b5d9-89d9a8c3f34a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_589bf1ed-fb96-4689-9edb-96be68e5794d" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_638406b9-3913-42b1-b5d9-89d9a8c3f34a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_638406b9-3913-42b1-b5d9-89d9a8c3f34a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_638406b9-3913-42b1-b5d9-89d9a8c3f34a" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_638406b9-3913-42b1-b5d9-89d9a8c3f34a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_58124c01-0202-483f-828b-85facf6a4851" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_638406b9-3913-42b1-b5d9-89d9a8c3f34a" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_58124c01-0202-483f-828b-85facf6a4851" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IPOMember_38151b9c-3423-443c-af24-debeb8f7ca34" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IPOMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_58124c01-0202-483f-828b-85facf6a4851" xlink:to="loc_us-gaap_IPOMember_38151b9c-3423-443c-af24-debeb8f7ca34" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_78d4c739-ed3f-45fa-ae2d-fae3829832db" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_589bf1ed-fb96-4689-9edb-96be68e5794d" xlink:to="loc_us-gaap_VestingAxis_78d4c739-ed3f-45fa-ae2d-fae3829832db" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_78d4c739-ed3f-45fa-ae2d-fae3829832db_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_78d4c739-ed3f-45fa-ae2d-fae3829832db" xlink:to="loc_us-gaap_VestingDomain_78d4c739-ed3f-45fa-ae2d-fae3829832db_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_00984cc0-07c8-4c43-9d22-61bf719b4216" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_78d4c739-ed3f-45fa-ae2d-fae3829832db" xlink:to="loc_us-gaap_VestingDomain_00984cc0-07c8-4c43-9d22-61bf719b4216" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_6bf0c492-8ae5-4755-b993-1159efb10d06" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_00984cc0-07c8-4c43-9d22-61bf719b4216" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_6bf0c492-8ae5-4755-b993-1159efb10d06" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_cb5e6d2d-519f-4775-8102-0aa0fa7ac277" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_00984cc0-07c8-4c43-9d22-61bf719b4216" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_cb5e6d2d-519f-4775-8102-0aa0fa7ac277" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_e5d01318-f626-4f9a-a81b-75b6da922434" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e60e5512-ba55-4fce-a4b5-0d1f229c6075" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_e5d01318-f626-4f9a-a81b-75b6da922434" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_627e5a3a-18af-4913-8785-0fd011dfe3d3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e60e5512-ba55-4fce-a4b5-0d1f229c6075" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_627e5a3a-18af-4913-8785-0fd011dfe3d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_5626c5b3-e165-45d1-b7c6-caa60acbd3d2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e60e5512-ba55-4fce-a4b5-0d1f229c6075" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_5626c5b3-e165-45d1-b7c6-caa60acbd3d2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_debc9b87-6605-414f-ac24-a82eccd57f04" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e60e5512-ba55-4fce-a4b5-0d1f229c6075" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_debc9b87-6605-414f-ac24-a82eccd57f04" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_e167816c-7c04-47a2-a965-0fee1ce41a5e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e60e5512-ba55-4fce-a4b5-0d1f229c6075" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_e167816c-7c04-47a2-a965-0fee1ce41a5e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares_53b29f28-fc56-4e8e-a391-a135b557dfa1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e60e5512-ba55-4fce-a4b5-0d1f229c6075" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares_53b29f28-fc56-4e8e-a391-a135b557dfa1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_365959c5-38fc-48df-996e-a18d449f269a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e60e5512-ba55-4fce-a4b5-0d1f229c6075" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_365959c5-38fc-48df-996e-a18d449f269a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_76e80959-4399-4154-b1ad-3088893e8eb1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e60e5512-ba55-4fce-a4b5-0d1f229c6075" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_76e80959-4399-4154-b1ad-3088893e8eb1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_NumberOfDaysForPaymentOfConsideration_0044319b-5125-4b38-8d4d-0cc79af3c639" xlink:href="gct-20231231.xsd#gct_NumberOfDaysForPaymentOfConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e60e5512-ba55-4fce-a4b5-0d1f229c6075" xlink:to="loc_gct_NumberOfDaysForPaymentOfConsideration_0044319b-5125-4b38-8d4d-0cc79af3c639" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_755ca6a7-2c67-4032-9f27-9786845aa929" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e60e5512-ba55-4fce-a4b5-0d1f229c6075" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_755ca6a7-2c67-4032-9f27-9786845aa929" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_2bedf495-b8ea-4dca-b259-b737852c61ec" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e60e5512-ba55-4fce-a4b5-0d1f229c6075" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_2bedf495-b8ea-4dca-b259-b737852c61ec" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_4e26884e-a3fd-4e09-b3f3-142c8572189e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e60e5512-ba55-4fce-a4b5-0d1f229c6075" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_4e26884e-a3fd-4e09-b3f3-142c8572189e" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_8e430327-9fb9-4e5e-b80c-7a773ac27242" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e60e5512-ba55-4fce-a4b5-0d1f229c6075" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_8e430327-9fb9-4e5e-b80c-7a773ac27242" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_01da713d-e6e0-4ad1-a8f1-0f9eb38c507d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e60e5512-ba55-4fce-a4b5-0d1f229c6075" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_01da713d-e6e0-4ad1-a8f1-0f9eb38c507d" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_NumberOfEmployeesReceivingRSUsGranted_242d4c77-dfe8-4c7e-a768-772fb04c7f60" xlink:href="gct-20231231.xsd#gct_NumberOfEmployeesReceivingRSUsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e60e5512-ba55-4fce-a4b5-0d1f229c6075" xlink:to="loc_gct_NumberOfEmployeesReceivingRSUsGranted_242d4c77-dfe8-4c7e-a768-772fb04c7f60" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_40b50fc1-a9dd-4602-8352-0ccc57bcdb57" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e60e5512-ba55-4fce-a4b5-0d1f229c6075" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_40b50fc1-a9dd-4602-8352-0ccc57bcdb57" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_09bd9798-10dd-44a6-a3f1-52ed8873deb8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e60e5512-ba55-4fce-a4b5-0d1f229c6075" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_09bd9798-10dd-44a6-a3f1-52ed8873deb8" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNotExercisableNumber_4d5e3afb-d4d0-4033-af9b-9666bacdc7d3" xlink:href="gct-20231231.xsd#gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNotExercisableNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e60e5512-ba55-4fce-a4b5-0d1f229c6075" xlink:to="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNotExercisableNumber_4d5e3afb-d4d0-4033-af9b-9666bacdc7d3" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_2bc607ba-0c4d-41ed-9dc6-5d7632f7ea17" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e60e5512-ba55-4fce-a4b5-0d1f229c6075" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_2bc607ba-0c4d-41ed-9dc6-5d7632f7ea17" xlink:type="arc" order="18"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/ShareBasedCompensationScheduleoftheestimatedfairvalueoftheshareoptionsgrantedDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#ShareBasedCompensationScheduleoftheestimatedfairvalueoftheshareoptionsgrantedDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/ShareBasedCompensationScheduleoftheestimatedfairvalueoftheshareoptionsgrantedDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_03e30d20-355c-4a79-83de-c247e206b804" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_6206291b-0589-46f2-917f-1ebfb5b027ec" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_03e30d20-355c-4a79-83de-c247e206b804" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_6206291b-0589-46f2-917f-1ebfb5b027ec" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_e2becd67-fe57-47f9-9bb9-7ee12af58a02" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_6206291b-0589-46f2-917f-1ebfb5b027ec" xlink:to="loc_srt_RangeAxis_e2becd67-fe57-47f9-9bb9-7ee12af58a02" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_e2becd67-fe57-47f9-9bb9-7ee12af58a02_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_e2becd67-fe57-47f9-9bb9-7ee12af58a02" xlink:to="loc_srt_RangeMember_e2becd67-fe57-47f9-9bb9-7ee12af58a02_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_c2fe3c2e-7a89-4860-9840-6aeaedfe6d5b" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_e2becd67-fe57-47f9-9bb9-7ee12af58a02" xlink:to="loc_srt_RangeMember_c2fe3c2e-7a89-4860-9840-6aeaedfe6d5b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_5378cf32-1066-4d89-a514-24529a77c2c0" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_c2fe3c2e-7a89-4860-9840-6aeaedfe6d5b" xlink:to="loc_srt_MinimumMember_5378cf32-1066-4d89-a514-24529a77c2c0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_8b784e96-7697-4d47-a684-dc81c99c142f" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_c2fe3c2e-7a89-4860-9840-6aeaedfe6d5b" xlink:to="loc_srt_MaximumMember_8b784e96-7697-4d47-a684-dc81c99c142f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_fcaf44f7-9e31-4c1d-a1e2-069c4d62b913" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_03e30d20-355c-4a79-83de-c247e206b804" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_fcaf44f7-9e31-4c1d-a1e2-069c4d62b913" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_52c1187f-4451-4cb4-8e58-828ce34c1d06" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_03e30d20-355c-4a79-83de-c247e206b804" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_52c1187f-4451-4cb4-8e58-828ce34c1d06" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_64a0d949-7330-4024-b051-492085fbe663" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_03e30d20-355c-4a79-83de-c247e206b804" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_64a0d949-7330-4024-b051-492085fbe663" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExercisePrice_74796d1c-3120-4221-a64e-f7258dbf772d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_03e30d20-355c-4a79-83de-c247e206b804" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExercisePrice_74796d1c-3120-4221-a64e-f7258dbf772d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsOfOrdinaryShare_ce69e174-f91f-46df-816a-645338e7d8e6" xlink:href="gct-20231231.xsd#gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsOfOrdinaryShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_03e30d20-355c-4a79-83de-c247e206b804" xlink:to="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsOfOrdinaryShare_ce69e174-f91f-46df-816a-645338e7d8e6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_dd4a63a9-f698-42cc-a20b-8c3b0bdacf59" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_03e30d20-355c-4a79-83de-c247e206b804" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_dd4a63a9-f698-42cc-a20b-8c3b0bdacf59" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/ShareBasedCompensationScheduleofthecompensationexpensesrecognizedDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#ShareBasedCompensationScheduleofthecompensationexpensesrecognizedDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/ShareBasedCompensationScheduleofthecompensationexpensesrecognizedDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_92fec0ab-4d69-4755-8113-81b5792fec98" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_34d4e046-1e0f-4160-aacd-e574bb8f6e70" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_92fec0ab-4d69-4755-8113-81b5792fec98" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_34d4e046-1e0f-4160-aacd-e574bb8f6e70" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_7a909a5f-7493-4d81-bbad-c394405d7f35" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_34d4e046-1e0f-4160-aacd-e574bb8f6e70" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_7a909a5f-7493-4d81-bbad-c394405d7f35" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_7a909a5f-7493-4d81-bbad-c394405d7f35_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_7a909a5f-7493-4d81-bbad-c394405d7f35" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_7a909a5f-7493-4d81-bbad-c394405d7f35_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_61debb6f-0070-4fa4-9383-c9a3e14a007d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_7a909a5f-7493-4d81-bbad-c394405d7f35" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_61debb6f-0070-4fa4-9383-c9a3e14a007d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_392661c6-531e-4478-874f-ae00d22f0965" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_61debb6f-0070-4fa4-9383-c9a3e14a007d" xlink:to="loc_us-gaap_CostOfSalesMember_392661c6-531e-4478-874f-ae00d22f0965" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpenseMember_18f674c5-0802-4263-b96e-bd7dbf7f414b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SellingAndMarketingExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_61debb6f-0070-4fa4-9383-c9a3e14a007d" xlink:to="loc_us-gaap_SellingAndMarketingExpenseMember_18f674c5-0802-4263-b96e-bd7dbf7f414b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_e65f8c1e-ac56-4f32-a723-37bfaf1b246f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_61debb6f-0070-4fa4-9383-c9a3e14a007d" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_e65f8c1e-ac56-4f32-a723-37bfaf1b246f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_15732514-5be4-47fc-b12f-0d6a61bb113f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ResearchAndDevelopmentExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_61debb6f-0070-4fa4-9383-c9a3e14a007d" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_15732514-5be4-47fc-b12f-0d6a61bb113f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_500dd34e-057a-4412-a697-0490a8a1fd1f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_34d4e046-1e0f-4160-aacd-e574bb8f6e70" xlink:to="loc_us-gaap_AwardTypeAxis_500dd34e-057a-4412-a697-0490a8a1fd1f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_500dd34e-057a-4412-a697-0490a8a1fd1f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_500dd34e-057a-4412-a697-0490a8a1fd1f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_500dd34e-057a-4412-a697-0490a8a1fd1f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d1c2c1f3-9f93-4f74-832a-d64916daf344" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_500dd34e-057a-4412-a697-0490a8a1fd1f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d1c2c1f3-9f93-4f74-832a-d64916daf344" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_d8498760-47a3-40c9-a49f-0e180d942c9c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d1c2c1f3-9f93-4f74-832a-d64916daf344" xlink:to="loc_us-gaap_EmployeeStockOptionMember_d8498760-47a3-40c9-a49f-0e180d942c9c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_3c737026-25d3-4668-92be-2407c45c13c2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d1c2c1f3-9f93-4f74-832a-d64916daf344" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_3c737026-25d3-4668-92be-2407c45c13c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_3f14b396-fea5-4771-ace6-ed61e053e3aa" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_92fec0ab-4d69-4755-8113-81b5792fec98" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_3f14b396-fea5-4771-ace6-ed61e053e3aa" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/ShareBasedCompensationScheduleoftherestrictedsharesDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#ShareBasedCompensationScheduleoftherestrictedsharesDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/ShareBasedCompensationScheduleoftherestrictedsharesDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5e9b71c4-82ca-4396-acd3-6cb44c1973a1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_1bc2de35-b165-4b71-b0b0-d4814231fac7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5e9b71c4-82ca-4396-acd3-6cb44c1973a1" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_1bc2de35-b165-4b71-b0b0-d4814231fac7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_ea4d670b-8515-4514-91d1-8d772df5a895" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_1bc2de35-b165-4b71-b0b0-d4814231fac7" xlink:to="loc_us-gaap_AwardTypeAxis_ea4d670b-8515-4514-91d1-8d772df5a895" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ea4d670b-8515-4514-91d1-8d772df5a895_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_ea4d670b-8515-4514-91d1-8d772df5a895" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ea4d670b-8515-4514-91d1-8d772df5a895_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_030b2b75-6c05-45c6-bdc9-2934d097e894" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_ea4d670b-8515-4514-91d1-8d772df5a895" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_030b2b75-6c05-45c6-bdc9-2934d097e894" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_4e39fcf7-369f-4777-a191-b2cbddfdafd1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_030b2b75-6c05-45c6-bdc9-2934d097e894" xlink:to="loc_us-gaap_RestrictedStockMember_4e39fcf7-369f-4777-a191-b2cbddfdafd1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_2b2c292c-41b2-4ef2-bedc-7c542684a195" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5e9b71c4-82ca-4396-acd3-6cb44c1973a1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_2b2c292c-41b2-4ef2-bedc-7c542684a195" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_39196159-274c-4d4e-af74-c9b73e559a2a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5e9b71c4-82ca-4396-acd3-6cb44c1973a1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_39196159-274c-4d4e-af74-c9b73e559a2a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_61db7745-6ca4-4528-a34c-68e9d1dab561" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5e9b71c4-82ca-4396-acd3-6cb44c1973a1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_61db7745-6ca4-4528-a34c-68e9d1dab561" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_d1e8887a-c489-4a21-8856-fbab6b00b352" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExpectToVested_bfdb1ce4-7a54-4800-a154-ed5ae80c20f4" xlink:href="gct-20231231.xsd#gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExpectToVested"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5e9b71c4-82ca-4396-acd3-6cb44c1973a1" xlink:to="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExpectToVested_bfdb1ce4-7a54-4800-a154-ed5ae80c20f4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_cb7eee55-eebd-4749-bd62-c3179168127c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5e9b71c4-82ca-4396-acd3-6cb44c1973a1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_cb7eee55-eebd-4749-bd62-c3179168127c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_bd56483f-6e89-4d3a-84e3-50a4fb96eaf3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5e9b71c4-82ca-4396-acd3-6cb44c1973a1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_bd56483f-6e89-4d3a-84e3-50a4fb96eaf3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_225244f1-e10d-4cb1-99d5-64cfaa681d59" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5e9b71c4-82ca-4396-acd3-6cb44c1973a1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_225244f1-e10d-4cb1-99d5-64cfaa681d59" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_cc0257a4-d66e-4e8f-a90c-70f5c9d5b740" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExpectToVestedWeightedAverageGrantDateFairValue_5708b67d-ecda-4cc5-a184-2e089ae68d47" xlink:href="gct-20231231.xsd#gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExpectToVestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5e9b71c4-82ca-4396-acd3-6cb44c1973a1" xlink:to="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExpectToVestedWeightedAverageGrantDateFairValue_5708b67d-ecda-4cc5-a184-2e089ae68d47" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/ShareBasedCompensationScheduleofrestrictedstockunitactivityDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#ShareBasedCompensationScheduleofrestrictedstockunitactivityDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/ShareBasedCompensationScheduleofrestrictedstockunitactivityDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6615ae2e-f14b-4e94-928e-ce0e92c8e071" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c3dff2c4-ccc1-4a3b-bca8-e1a2b940e221" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6615ae2e-f14b-4e94-928e-ce0e92c8e071" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c3dff2c4-ccc1-4a3b-bca8-e1a2b940e221" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_5349c54a-5169-490c-9a03-1e456f020173" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c3dff2c4-ccc1-4a3b-bca8-e1a2b940e221" xlink:to="loc_us-gaap_AwardTypeAxis_5349c54a-5169-490c-9a03-1e456f020173" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_5349c54a-5169-490c-9a03-1e456f020173_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_5349c54a-5169-490c-9a03-1e456f020173" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_5349c54a-5169-490c-9a03-1e456f020173_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_96fdfb64-bb88-4de3-a8e5-f28bef9a2a8b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_5349c54a-5169-490c-9a03-1e456f020173" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_96fdfb64-bb88-4de3-a8e5-f28bef9a2a8b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_e25f14b3-9def-4ed5-9400-2739326e5797" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_96fdfb64-bb88-4de3-a8e5-f28bef9a2a8b" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_e25f14b3-9def-4ed5-9400-2739326e5797" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_89a7f962-e729-4313-9bdd-960573dacdd7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6615ae2e-f14b-4e94-928e-ce0e92c8e071" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_89a7f962-e729-4313-9bdd-960573dacdd7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_832b2049-14fd-40fe-986b-3aa66f9e7f3e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_89a7f962-e729-4313-9bdd-960573dacdd7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_832b2049-14fd-40fe-986b-3aa66f9e7f3e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_8df9f5a1-0de1-412e-a9d0-312ff88b9c94" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_89a7f962-e729-4313-9bdd-960573dacdd7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_8df9f5a1-0de1-412e-a9d0-312ff88b9c94" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_a709a7b6-419f-409a-b714-e8a9a48b9449" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateExercisePriceValueRollForwardAbstract_5c34d208-1532-44a7-905e-88f8ad567009" xlink:href="gct-20231231.xsd#gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateExercisePriceValueRollForwardAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6615ae2e-f14b-4e94-928e-ce0e92c8e071" xlink:to="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateExercisePriceValueRollForwardAbstract_5c34d208-1532-44a7-905e-88f8ad567009" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedOutstandingWeightedAverageGrantDateExercisePrice_595c3f65-067d-4fc6-8ec5-89260e38e9d1" xlink:href="gct-20231231.xsd#gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedOutstandingWeightedAverageGrantDateExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateExercisePriceValueRollForwardAbstract_5c34d208-1532-44a7-905e-88f8ad567009" xlink:to="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedOutstandingWeightedAverageGrantDateExercisePrice_595c3f65-067d-4fc6-8ec5-89260e38e9d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateExercisePrice_1b383c78-1598-4747-8874-14b728e6bc0e" xlink:href="gct-20231231.xsd#gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateExercisePriceValueRollForwardAbstract_5c34d208-1532-44a7-905e-88f8ad567009" xlink:to="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateExercisePrice_1b383c78-1598-4747-8874-14b728e6bc0e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedOutstandingWeightedAverageGrantDateExercisePrice_12502bab-1569-41ad-a501-0dcf3dead313" xlink:href="gct-20231231.xsd#gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedOutstandingWeightedAverageGrantDateExercisePrice"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_3f604860-02fc-41e3-ab3f-a2bd6db94ca1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6615ae2e-f14b-4e94-928e-ce0e92c8e071" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_3f604860-02fc-41e3-ab3f-a2bd6db94ca1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_3c73be39-baa0-491f-ba0a-f1cbef0b582f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_3f604860-02fc-41e3-ab3f-a2bd6db94ca1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_3c73be39-baa0-491f-ba0a-f1cbef0b582f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_2468d8b5-5638-4fc1-8bd1-471f80ee6dbd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_3f604860-02fc-41e3-ab3f-a2bd6db94ca1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_2468d8b5-5638-4fc1-8bd1-471f80ee6dbd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_03899e8e-f59d-4c5a-a09e-bd00a520a90a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_6b2173b8-4893-4ebf-9cde-6d46f2e1c685" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6615ae2e-f14b-4e94-928e-ce0e92c8e071" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_6b2173b8-4893-4ebf-9cde-6d46f2e1c685" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedExercisableNumber_a5f3f5f6-7b04-42cb-8ee9-c08bb67fbbdf" xlink:href="gct-20231231.xsd#gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedExercisableNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_6b2173b8-4893-4ebf-9cde-6d46f2e1c685" xlink:to="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedExercisableNumber_a5f3f5f6-7b04-42cb-8ee9-c08bb67fbbdf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisableWeightedAverageExercisePrice_323759d0-cfdf-4ce8-8987-a6e6730720c5" xlink:href="gct-20231231.xsd#gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisableWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_6b2173b8-4893-4ebf-9cde-6d46f2e1c685" xlink:to="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisableWeightedAverageExercisePrice_323759d0-cfdf-4ce8-8987-a6e6730720c5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisableWeightedAverageGrantDateFairValue_75133f39-a39b-4dc1-86ac-894ab8b03473" xlink:href="gct-20231231.xsd#gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisableWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_6b2173b8-4893-4ebf-9cde-6d46f2e1c685" xlink:to="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisableWeightedAverageGrantDateFairValue_75133f39-a39b-4dc1-86ac-894ab8b03473" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageRemainingContractualTerms_89d86ce1-351b-47d5-a063-a6a6b6714c2e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageRemainingContractualTerms"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_6b2173b8-4893-4ebf-9cde-6d46f2e1c685" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageRemainingContractualTerms_89d86ce1-351b-47d5-a063-a6a6b6714c2e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentOtherThanOptionsExercisableWeightedAverageRemainingContractualTerm_d97b9d2c-8eff-477e-bd40-c1323e6e224e" xlink:href="gct-20231231.xsd#gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentOtherThanOptionsExercisableWeightedAverageRemainingContractualTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_6b2173b8-4893-4ebf-9cde-6d46f2e1c685" xlink:to="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentOtherThanOptionsExercisableWeightedAverageRemainingContractualTerm_d97b9d2c-8eff-477e-bd40-c1323e6e224e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueOutstanding_ac25c899-7538-46d4-8b91-b4ae592c70f8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_6b2173b8-4893-4ebf-9cde-6d46f2e1c685" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueOutstanding_ac25c899-7538-46d4-8b91-b4ae592c70f8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueExercisable_da735c86-2652-4e0b-ac5b-be2346afef95" xlink:href="gct-20231231.xsd#gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueExercisable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_6b2173b8-4893-4ebf-9cde-6d46f2e1c685" xlink:to="loc_gct_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueExercisable_da735c86-2652-4e0b-ac5b-be2346afef95" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/WarrantAdditionalInformationDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#WarrantAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/WarrantAdditionalInformationDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_011c95c2-9209-4ec9-a5b7-adcf19137c98" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_59e397ec-06f4-4883-8f3e-4ea6f677ff63" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_011c95c2-9209-4ec9-a5b7-adcf19137c98" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_59e397ec-06f4-4883-8f3e-4ea6f677ff63" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_bd7a38c8-b395-4216-823a-2e46e09a3a87" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_59e397ec-06f4-4883-8f3e-4ea6f677ff63" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_bd7a38c8-b395-4216-823a-2e46e09a3a87" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_bd7a38c8-b395-4216-823a-2e46e09a3a87_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_bd7a38c8-b395-4216-823a-2e46e09a3a87" xlink:to="loc_us-gaap_RelatedPartyDomain_bd7a38c8-b395-4216-823a-2e46e09a3a87_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_b1f93e0b-c171-493e-a82c-43ef0a620172" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_bd7a38c8-b395-4216-823a-2e46e09a3a87" xlink:to="loc_us-gaap_RelatedPartyDomain_b1f93e0b-c171-493e-a82c-43ef0a620172" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_UnderwriterMember_91218d79-29fd-47fa-bc6a-59cc89848fa1" xlink:href="gct-20231231.xsd#gct_UnderwriterMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_b1f93e0b-c171-493e-a82c-43ef0a620172" xlink:to="loc_gct_UnderwriterMember_91218d79-29fd-47fa-bc6a-59cc89848fa1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_046feb87-971b-407d-975d-c628ddc42429" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_59e397ec-06f4-4883-8f3e-4ea6f677ff63" xlink:to="loc_us-gaap_StatementClassOfStockAxis_046feb87-971b-407d-975d-c628ddc42429" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_046feb87-971b-407d-975d-c628ddc42429_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_046feb87-971b-407d-975d-c628ddc42429" xlink:to="loc_us-gaap_ClassOfStockDomain_046feb87-971b-407d-975d-c628ddc42429_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_5d9ddfff-ef30-4836-affb-97a74b979369" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_046feb87-971b-407d-975d-c628ddc42429" xlink:to="loc_us-gaap_ClassOfStockDomain_5d9ddfff-ef30-4836-affb-97a74b979369" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_b499334b-85bb-4390-9bb2-e9f586146f6f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_5d9ddfff-ef30-4836-affb-97a74b979369" xlink:to="loc_us-gaap_CommonClassAMember_b499334b-85bb-4390-9bb2-e9f586146f6f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_9112368d-e349-494c-94bc-33a6ebd5a672" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_59e397ec-06f4-4883-8f3e-4ea6f677ff63" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_9112368d-e349-494c-94bc-33a6ebd5a672" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_9112368d-e349-494c-94bc-33a6ebd5a672_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_9112368d-e349-494c-94bc-33a6ebd5a672" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_9112368d-e349-494c-94bc-33a6ebd5a672_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_59b768b0-dd4e-414c-8061-ae676a7c533c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_9112368d-e349-494c-94bc-33a6ebd5a672" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_59b768b0-dd4e-414c-8061-ae676a7c533c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IPOMember_c4503349-4998-4eb2-b3a0-d64ed27912b4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IPOMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_59b768b0-dd4e-414c-8061-ae676a7c533c" xlink:to="loc_us-gaap_IPOMember_c4503349-4998-4eb2-b3a0-d64ed27912b4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ClassOfWarrantOrRightPercentageOfSecuritiesCalledByWarrantsOrRights_33f0a991-ca25-4201-b989-1630365ae4dd" xlink:href="gct-20231231.xsd#gct_ClassOfWarrantOrRightPercentageOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_011c95c2-9209-4ec9-a5b7-adcf19137c98" xlink:to="loc_gct_ClassOfWarrantOrRightPercentageOfSecuritiesCalledByWarrantsOrRights_33f0a991-ca25-4201-b989-1630365ae4dd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_33b6214d-66e4-4493-bdf6-196eb993ca4d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_011c95c2-9209-4ec9-a5b7-adcf19137c98" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_33b6214d-66e4-4493-bdf6-196eb993ca4d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PercentageOfExercisePriceToPublicOfferingPrice_f9a7cd89-8f6a-4327-95eb-4c5aec0f0679" xlink:href="gct-20231231.xsd#gct_PercentageOfExercisePriceToPublicOfferingPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_011c95c2-9209-4ec9-a5b7-adcf19137c98" xlink:to="loc_gct_PercentageOfExercisePriceToPublicOfferingPrice_f9a7cd89-8f6a-4327-95eb-4c5aec0f0679" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssuedPricePerShare_4c2b1906-3983-4cfe-a8b2-198d87e429a5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharesIssuedPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_011c95c2-9209-4ec9-a5b7-adcf19137c98" xlink:to="loc_us-gaap_SharesIssuedPricePerShare_4c2b1906-3983-4cfe-a8b2-198d87e429a5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_3f7bc1a5-cc24-457b-9946-a4ede8fdd275" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_011c95c2-9209-4ec9-a5b7-adcf19137c98" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_3f7bc1a5-cc24-457b-9946-a4ede8fdd275" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_58e4b45b-e2e3-4af1-af22-c6a321649c41" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_011c95c2-9209-4ec9-a5b7-adcf19137c98" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_58e4b45b-e2e3-4af1-af22-c6a321649c41" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued_44b20317-51ce-45f6-81fa-33028eb4b590" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_011c95c2-9209-4ec9-a5b7-adcf19137c98" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued_44b20317-51ce-45f6-81fa-33028eb4b590" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/WarrantScheduleoftheFairvalueoftheWarrantupontheissuanceDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#WarrantScheduleoftheFairvalueoftheWarrantupontheissuanceDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/WarrantScheduleoftheFairvalueoftheWarrantupontheissuanceDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_30bacf6f-1b16-42c1-a844-9e49b254eb78" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_57c14631-c62d-4828-9692-c547f8221492" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_30bacf6f-1b16-42c1-a844-9e49b254eb78" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_57c14631-c62d-4828-9692-c547f8221492" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_50e93876-3f74-43c3-8fa3-f6924d862ac6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_57c14631-c62d-4828-9692-c547f8221492" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_50e93876-3f74-43c3-8fa3-f6924d862ac6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_50e93876-3f74-43c3-8fa3-f6924d862ac6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_50e93876-3f74-43c3-8fa3-f6924d862ac6" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_50e93876-3f74-43c3-8fa3-f6924d862ac6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_5bc9a0cc-0ce8-43aa-af5b-58e667e57833" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_50e93876-3f74-43c3-8fa3-f6924d862ac6" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_5bc9a0cc-0ce8-43aa-af5b-58e667e57833" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_8533ddf0-886c-427d-8299-77327b34b5b2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MeasurementInputRiskFreeInterestRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_5bc9a0cc-0ce8-43aa-af5b-58e667e57833" xlink:to="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_8533ddf0-886c-427d-8299-77327b34b5b2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputPriceVolatilityMember_d6ffc99b-59bb-4433-917e-827bbf9f2a90" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MeasurementInputPriceVolatilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_5bc9a0cc-0ce8-43aa-af5b-58e667e57833" xlink:to="loc_us-gaap_MeasurementInputPriceVolatilityMember_d6ffc99b-59bb-4433-917e-827bbf9f2a90" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputExpectedDividendRateMember_b50f285e-32a3-4d9b-9ba1-929d976b918d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MeasurementInputExpectedDividendRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_5bc9a0cc-0ce8-43aa-af5b-58e667e57833" xlink:to="loc_us-gaap_MeasurementInputExpectedDividendRateMember_b50f285e-32a3-4d9b-9ba1-929d976b918d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputSharePriceMember_e45e1a25-696b-400f-9cea-2eddf0124c39" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MeasurementInputSharePriceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_5bc9a0cc-0ce8-43aa-af5b-58e667e57833" xlink:to="loc_us-gaap_MeasurementInputSharePriceMember_e45e1a25-696b-400f-9cea-2eddf0124c39" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputExpectedTermMember_ca9ad350-7bb3-4aff-b6dd-5d4f05ec42d5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MeasurementInputExpectedTermMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_5bc9a0cc-0ce8-43aa-af5b-58e667e57833" xlink:to="loc_us-gaap_MeasurementInputExpectedTermMember_ca9ad350-7bb3-4aff-b6dd-5d4f05ec42d5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstandingMeasurementInput_2cc50411-a50a-4055-a750-8990667e4390" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_WarrantsAndRightsOutstandingMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_30bacf6f-1b16-42c1-a844-9e49b254eb78" xlink:to="loc_us-gaap_WarrantsAndRightsOutstandingMeasurementInput_2cc50411-a50a-4055-a750-8990667e4390" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstandingTerm_ba3b7e10-bb07-457a-8740-50f623d5d3f7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_WarrantsAndRightsOutstandingTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_30bacf6f-1b16-42c1-a844-9e49b254eb78" xlink:to="loc_us-gaap_WarrantsAndRightsOutstandingTerm_ba3b7e10-bb07-457a-8740-50f623d5d3f7" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/IncomeTaxAdditionalInformationDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#IncomeTaxAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/IncomeTaxAdditionalInformationDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_gct_IncomeTaxDisclosureLineItems_e44d29b1-5a0f-4611-b846-0a3743226b41" xlink:href="gct-20231231.xsd#gct_IncomeTaxDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_IncomeTaxDisclosureTable_65a6dd35-f577-43d9-ac34-48208d6cdce6" xlink:href="gct-20231231.xsd#gct_IncomeTaxDisclosureTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_gct_IncomeTaxDisclosureLineItems_e44d29b1-5a0f-4611-b846-0a3743226b41" xlink:to="loc_gct_IncomeTaxDisclosureTable_65a6dd35-f577-43d9-ac34-48208d6cdce6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_3b17b080-5628-497d-b66e-44c752546d98" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_IncomeTaxDisclosureTable_65a6dd35-f577-43d9-ac34-48208d6cdce6" xlink:to="loc_srt_StatementGeographicalAxis_3b17b080-5628-497d-b66e-44c752546d98" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_3b17b080-5628-497d-b66e-44c752546d98_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_3b17b080-5628-497d-b66e-44c752546d98" xlink:to="loc_srt_SegmentGeographicalDomain_3b17b080-5628-497d-b66e-44c752546d98_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_7debb2be-1d48-40c5-b548-0fc2458756e4" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_3b17b080-5628-497d-b66e-44c752546d98" xlink:to="loc_srt_SegmentGeographicalDomain_7debb2be-1d48-40c5-b548-0fc2458756e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_HK_445fc46d-83fa-4574-8e50-927dc29b826a" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_HK"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_7debb2be-1d48-40c5-b548-0fc2458756e4" xlink:to="loc_country_HK_445fc46d-83fa-4574-8e50-927dc29b826a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_CN_5460821d-6018-4d5d-8715-59aa2e15e931" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_CN"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_7debb2be-1d48-40c5-b548-0fc2458756e4" xlink:to="loc_country_CN_5460821d-6018-4d5d-8715-59aa2e15e931" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_eb421c3d-2dfd-4b34-b66a-4a06d476b476" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_7debb2be-1d48-40c5-b548-0fc2458756e4" xlink:to="loc_country_US_eb421c3d-2dfd-4b34-b66a-4a06d476b476" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_GB_a2cb55ea-f212-41f1-a9cb-8fe674f205f6" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_GB"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_7debb2be-1d48-40c5-b548-0fc2458756e4" xlink:to="loc_country_GB_a2cb55ea-f212-41f1-a9cb-8fe674f205f6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_DE_9f3d105e-e170-4188-af7c-f7915c5267ba" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_DE"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_7debb2be-1d48-40c5-b548-0fc2458756e4" xlink:to="loc_country_DE_9f3d105e-e170-4188-af7c-f7915c5267ba" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_CA_5dd32e56-cbc1-4ba3-badd-225804ed5efd" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_CA"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_7debb2be-1d48-40c5-b548-0fc2458756e4" xlink:to="loc_country_CA_5dd32e56-cbc1-4ba3-badd-225804ed5efd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ProfitRangeAxis_9f7e339e-33e5-48bb-bdec-395f5c1145bf" xlink:href="gct-20231231.xsd#gct_ProfitRangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_IncomeTaxDisclosureTable_65a6dd35-f577-43d9-ac34-48208d6cdce6" xlink:to="loc_gct_ProfitRangeAxis_9f7e339e-33e5-48bb-bdec-395f5c1145bf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ProfitRangeDomain_9f7e339e-33e5-48bb-bdec-395f5c1145bf_default" xlink:href="gct-20231231.xsd#gct_ProfitRangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_gct_ProfitRangeAxis_9f7e339e-33e5-48bb-bdec-395f5c1145bf" xlink:to="loc_gct_ProfitRangeDomain_9f7e339e-33e5-48bb-bdec-395f5c1145bf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ProfitRangeDomain_39375103-ec84-46ad-9fdf-50c2f774a261" xlink:href="gct-20231231.xsd#gct_ProfitRangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_gct_ProfitRangeAxis_9f7e339e-33e5-48bb-bdec-395f5c1145bf" xlink:to="loc_gct_ProfitRangeDomain_39375103-ec84-46ad-9fdf-50c2f774a261" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ProfitAboveTwoMillionHonKongDollarMember_4e97591c-54a1-497e-81ad-f7a20ecfdbcf" xlink:href="gct-20231231.xsd#gct_ProfitAboveTwoMillionHonKongDollarMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ProfitRangeDomain_39375103-ec84-46ad-9fdf-50c2f774a261" xlink:to="loc_gct_ProfitAboveTwoMillionHonKongDollarMember_4e97591c-54a1-497e-81ad-f7a20ecfdbcf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ProfitBelowTwoMillionHongKongDollarMember_cbbedaf7-6fc5-41ed-857e-14f8ecb0c37c" xlink:href="gct-20231231.xsd#gct_ProfitBelowTwoMillionHongKongDollarMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ProfitRangeDomain_39375103-ec84-46ad-9fdf-50c2f774a261" xlink:to="loc_gct_ProfitBelowTwoMillionHongKongDollarMember_cbbedaf7-6fc5-41ed-857e-14f8ecb0c37c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxPeriodAxis_199c2508-b1bb-4c51-9d4f-a9bbd5aa26f1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TaxPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_IncomeTaxDisclosureTable_65a6dd35-f577-43d9-ac34-48208d6cdce6" xlink:to="loc_us-gaap_TaxPeriodAxis_199c2508-b1bb-4c51-9d4f-a9bbd5aa26f1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxPeriodDomain_199c2508-b1bb-4c51-9d4f-a9bbd5aa26f1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TaxPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TaxPeriodAxis_199c2508-b1bb-4c51-9d4f-a9bbd5aa26f1" xlink:to="loc_us-gaap_TaxPeriodDomain_199c2508-b1bb-4c51-9d4f-a9bbd5aa26f1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxPeriodDomain_2f2466b4-46e9-405d-b2b8-7f093156db75" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TaxPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TaxPeriodAxis_199c2508-b1bb-4c51-9d4f-a9bbd5aa26f1" xlink:to="loc_us-gaap_TaxPeriodDomain_2f2466b4-46e9-405d-b2b8-7f093156db75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_FromTaxYear2019To2021Member_6deb90d7-0bd5-4ff9-9e65-9f1d34d9e630" xlink:href="gct-20231231.xsd#gct_FromTaxYear2019To2021Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxPeriodDomain_2f2466b4-46e9-405d-b2b8-7f093156db75" xlink:to="loc_gct_FromTaxYear2019To2021Member_6deb90d7-0bd5-4ff9-9e65-9f1d34d9e630" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_FromTaxYear2022To2024Member_c8572269-64b3-4d0e-aabf-c0f343bb3759" xlink:href="gct-20231231.xsd#gct_FromTaxYear2022To2024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxPeriodDomain_2f2466b4-46e9-405d-b2b8-7f093156db75" xlink:to="loc_gct_FromTaxYear2022To2024Member_c8572269-64b3-4d0e-aabf-c0f343bb3759" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_OperatingLossCarryForwardsExpirationPeriodAxis_8743b06e-32c5-4ed1-84e4-66a84ee01468" xlink:href="gct-20231231.xsd#gct_OperatingLossCarryForwardsExpirationPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_IncomeTaxDisclosureTable_65a6dd35-f577-43d9-ac34-48208d6cdce6" xlink:to="loc_gct_OperatingLossCarryForwardsExpirationPeriodAxis_8743b06e-32c5-4ed1-84e4-66a84ee01468" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_OperatingLossCarryForwardsExpirationPeriodDomain_8743b06e-32c5-4ed1-84e4-66a84ee01468_default" xlink:href="gct-20231231.xsd#gct_OperatingLossCarryForwardsExpirationPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_gct_OperatingLossCarryForwardsExpirationPeriodAxis_8743b06e-32c5-4ed1-84e4-66a84ee01468" xlink:to="loc_gct_OperatingLossCarryForwardsExpirationPeriodDomain_8743b06e-32c5-4ed1-84e4-66a84ee01468_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_OperatingLossCarryForwardsExpirationPeriodDomain_8d44a22b-2b69-42d2-a503-ae1b629f3682" xlink:href="gct-20231231.xsd#gct_OperatingLossCarryForwardsExpirationPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_gct_OperatingLossCarryForwardsExpirationPeriodAxis_8743b06e-32c5-4ed1-84e4-66a84ee01468" xlink:to="loc_gct_OperatingLossCarryForwardsExpirationPeriodDomain_8d44a22b-2b69-42d2-a503-ae1b629f3682" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ExpirableTaxYear2023Member_92c63921-7a44-4036-bb2a-f57155dbae59" xlink:href="gct-20231231.xsd#gct_ExpirableTaxYear2023Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_OperatingLossCarryForwardsExpirationPeriodDomain_8d44a22b-2b69-42d2-a503-ae1b629f3682" xlink:to="loc_gct_ExpirableTaxYear2023Member_92c63921-7a44-4036-bb2a-f57155dbae59" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ExpirableTaxYear2024Member_883e0f96-1622-4073-9d0a-3217eddaea6a" xlink:href="gct-20231231.xsd#gct_ExpirableTaxYear2024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_OperatingLossCarryForwardsExpirationPeriodDomain_8d44a22b-2b69-42d2-a503-ae1b629f3682" xlink:to="loc_gct_ExpirableTaxYear2024Member_883e0f96-1622-4073-9d0a-3217eddaea6a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ExpirableTaxYear2025Member_632801a1-8b06-4313-b3e1-0b4311ff65ff" xlink:href="gct-20231231.xsd#gct_ExpirableTaxYear2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_OperatingLossCarryForwardsExpirationPeriodDomain_8d44a22b-2b69-42d2-a503-ae1b629f3682" xlink:to="loc_gct_ExpirableTaxYear2025Member_632801a1-8b06-4313-b3e1-0b4311ff65ff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ExpirableTaxYear2026Member_268c7a9a-1dfb-401f-a7de-cffc36d60f9b" xlink:href="gct-20231231.xsd#gct_ExpirableTaxYear2026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_OperatingLossCarryForwardsExpirationPeriodDomain_8d44a22b-2b69-42d2-a503-ae1b629f3682" xlink:to="loc_gct_ExpirableTaxYear2026Member_268c7a9a-1dfb-401f-a7de-cffc36d60f9b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ExpirableTaxYear2027Member_748c498b-7587-466c-b503-480a834508e0" xlink:href="gct-20231231.xsd#gct_ExpirableTaxYear2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_OperatingLossCarryForwardsExpirationPeriodDomain_8d44a22b-2b69-42d2-a503-ae1b629f3682" xlink:to="loc_gct_ExpirableTaxYear2027Member_748c498b-7587-466c-b503-480a834508e0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ExpirableTaxYear2028Member_9ad35a46-d6ff-42e5-b854-92b4cde8a725" xlink:href="gct-20231231.xsd#gct_ExpirableTaxYear2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_OperatingLossCarryForwardsExpirationPeriodDomain_8d44a22b-2b69-42d2-a503-ae1b629f3682" xlink:to="loc_gct_ExpirableTaxYear2028Member_9ad35a46-d6ff-42e5-b854-92b4cde8a725" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ExpirableTaxYear2037Member_4f14bc18-d1ef-431a-b0f9-d42408eff5fe" xlink:href="gct-20231231.xsd#gct_ExpirableTaxYear2037Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_OperatingLossCarryForwardsExpirationPeriodDomain_8d44a22b-2b69-42d2-a503-ae1b629f3682" xlink:to="loc_gct_ExpirableTaxYear2037Member_4f14bc18-d1ef-431a-b0f9-d42408eff5fe" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowanceByDeferredTaxAssetAxis_5978af77-61c6-4a21-9f44-c8e1da7a11f3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ValuationAllowanceByDeferredTaxAssetAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_IncomeTaxDisclosureTable_65a6dd35-f577-43d9-ac34-48208d6cdce6" xlink:to="loc_us-gaap_ValuationAllowanceByDeferredTaxAssetAxis_5978af77-61c6-4a21-9f44-c8e1da7a11f3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetDomain_5978af77-61c6-4a21-9f44-c8e1da7a11f3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredTaxAssetDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationAllowanceByDeferredTaxAssetAxis_5978af77-61c6-4a21-9f44-c8e1da7a11f3" xlink:to="loc_us-gaap_DeferredTaxAssetDomain_5978af77-61c6-4a21-9f44-c8e1da7a11f3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetDomain_bf8103dd-70de-42e5-8315-ded12a2dabc5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredTaxAssetDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationAllowanceByDeferredTaxAssetAxis_5978af77-61c6-4a21-9f44-c8e1da7a11f3" xlink:to="loc_us-gaap_DeferredTaxAssetDomain_bf8103dd-70de-42e5-8315-ded12a2dabc5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_DeferredTaxAssetSubsidiariesAndVieMember_9ce7eec3-f45f-4ffc-ac31-aebad90a946b" xlink:href="gct-20231231.xsd#gct_DeferredTaxAssetSubsidiariesAndVieMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredTaxAssetDomain_bf8103dd-70de-42e5-8315-ded12a2dabc5" xlink:to="loc_gct_DeferredTaxAssetSubsidiariesAndVieMember_9ce7eec3-f45f-4ffc-ac31-aebad90a946b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_TaxLawAxis_b1b8f387-4b50-4dd4-a3e2-fac615fbfe1c" xlink:href="gct-20231231.xsd#gct_TaxLawAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_IncomeTaxDisclosureTable_65a6dd35-f577-43d9-ac34-48208d6cdce6" xlink:to="loc_gct_TaxLawAxis_b1b8f387-4b50-4dd4-a3e2-fac615fbfe1c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_TaxLawDomain_b1b8f387-4b50-4dd4-a3e2-fac615fbfe1c_default" xlink:href="gct-20231231.xsd#gct_TaxLawDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_gct_TaxLawAxis_b1b8f387-4b50-4dd4-a3e2-fac615fbfe1c" xlink:to="loc_gct_TaxLawDomain_b1b8f387-4b50-4dd4-a3e2-fac615fbfe1c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_TaxLawDomain_dcdf5e7e-e463-4612-8a2b-d5e490bab44c" xlink:href="gct-20231231.xsd#gct_TaxLawDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_gct_TaxLawAxis_b1b8f387-4b50-4dd4-a3e2-fac615fbfe1c" xlink:to="loc_gct_TaxLawDomain_dcdf5e7e-e463-4612-8a2b-d5e490bab44c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PrcTaxAdministrationAndCollectionLawMember_9f308810-ef15-4d27-8766-48f6e1a2a6bb" xlink:href="gct-20231231.xsd#gct_PrcTaxAdministrationAndCollectionLawMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_TaxLawDomain_dcdf5e7e-e463-4612-8a2b-d5e490bab44c" xlink:to="loc_gct_PrcTaxAdministrationAndCollectionLawMember_9f308810-ef15-4d27-8766-48f6e1a2a6bb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_86eb3333-9089-4727-96e5-bee5257d6433" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_IncomeTaxDisclosureTable_65a6dd35-f577-43d9-ac34-48208d6cdce6" xlink:to="loc_srt_RangeAxis_86eb3333-9089-4727-96e5-bee5257d6433" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_86eb3333-9089-4727-96e5-bee5257d6433_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_86eb3333-9089-4727-96e5-bee5257d6433" xlink:to="loc_srt_RangeMember_86eb3333-9089-4727-96e5-bee5257d6433_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_612e3b67-ce59-4c90-a685-632fac1f7621" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_86eb3333-9089-4727-96e5-bee5257d6433" xlink:to="loc_srt_RangeMember_612e3b67-ce59-4c90-a685-632fac1f7621" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_3cf0e8dc-4bdc-4964-9372-4a17c5b35fb8" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_612e3b67-ce59-4c90-a685-632fac1f7621" xlink:to="loc_srt_MinimumMember_3cf0e8dc-4bdc-4964-9372-4a17c5b35fb8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_e0f93631-f331-4520-86e3-d5cbc71bfd99" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_612e3b67-ce59-4c90-a685-632fac1f7621" xlink:to="loc_srt_MaximumMember_e0f93631-f331-4520-86e3-d5cbc71bfd99" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_48c4f1b4-bdc9-4898-93d7-0e7106d622b1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_IncomeTaxDisclosureLineItems_e44d29b1-5a0f-4611-b846-0a3743226b41" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_48c4f1b4-bdc9-4898-93d7-0e7106d622b1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_WithholdInIncomeTaxRateOnDividends_55f60f0d-c6d9-4909-8e81-d0616e7a6f9b" xlink:href="gct-20231231.xsd#gct_WithholdInIncomeTaxRateOnDividends"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_IncomeTaxDisclosureLineItems_e44d29b1-5a0f-4611-b846-0a3743226b41" xlink:to="loc_gct_WithholdInIncomeTaxRateOnDividends_55f60f0d-c6d9-4909-8e81-d0616e7a6f9b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromSubsidiariesBeforeTax_4d4f0902-bb5b-4bf1-89f9-37d6aa1214f3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeLossFromSubsidiariesBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_IncomeTaxDisclosureLineItems_e44d29b1-5a0f-4611-b846-0a3743226b41" xlink:to="loc_us-gaap_IncomeLossFromSubsidiariesBeforeTax_4d4f0902-bb5b-4bf1-89f9-37d6aa1214f3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_EffectiveIncomeTaxRateReconciliationPreferentialTaxRatePercentage_1d2e5916-e141-441d-9024-231f43728791" xlink:href="gct-20231231.xsd#gct_EffectiveIncomeTaxRateReconciliationPreferentialTaxRatePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_IncomeTaxDisclosureLineItems_e44d29b1-5a0f-4611-b846-0a3743226b41" xlink:to="loc_gct_EffectiveIncomeTaxRateReconciliationPreferentialTaxRatePercentage_1d2e5916-e141-441d-9024-231f43728791" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxLiabilityNotRecognizedAmountOfUnrecognizedDeferredTaxLiabilityUndistributedEarningsOfForeignSubsidiaries_d2589384-4258-47ba-86f9-ef047032cc4a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredTaxLiabilityNotRecognizedAmountOfUnrecognizedDeferredTaxLiabilityUndistributedEarningsOfForeignSubsidiaries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_IncomeTaxDisclosureLineItems_e44d29b1-5a0f-4611-b846-0a3743226b41" xlink:to="loc_us-gaap_DeferredTaxLiabilityNotRecognizedAmountOfUnrecognizedDeferredTaxLiabilityUndistributedEarningsOfForeignSubsidiaries_d2589384-4258-47ba-86f9-ef047032cc4a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwards_741d19c3-378b-42fe-a2c0-f23c9d7b1d31" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLossCarryforwards"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_IncomeTaxDisclosureLineItems_e44d29b1-5a0f-4611-b846-0a3743226b41" xlink:to="loc_us-gaap_OperatingLossCarryforwards_741d19c3-378b-42fe-a2c0-f23c9d7b1d31" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsValuationAllowance_9ecf4048-a741-4a1d-866c-2bd97cfc2534" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredTaxAssetsValuationAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_IncomeTaxDisclosureLineItems_e44d29b1-5a0f-4611-b846-0a3743226b41" xlink:to="loc_us-gaap_DeferredTaxAssetsValuationAllowance_9ecf4048-a741-4a1d-866c-2bd97cfc2534" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecognizedTaxBenefits_439c1a57-91fe-4e31-a2f2-563ec4833917" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_UnrecognizedTaxBenefits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_IncomeTaxDisclosureLineItems_e44d29b1-5a0f-4611-b846-0a3743226b41" xlink:to="loc_us-gaap_UnrecognizedTaxBenefits_439c1a57-91fe-4e31-a2f2-563ec4833917" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_UnrecognizedTaxBenefitsIncreaseResultingFromTransferPricingAdjustment_0e82d7b8-64d1-4d0c-b989-ac1915727583" xlink:href="gct-20231231.xsd#gct_UnrecognizedTaxBenefitsIncreaseResultingFromTransferPricingAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_IncomeTaxDisclosureLineItems_e44d29b1-5a0f-4611-b846-0a3743226b41" xlink:to="loc_gct_UnrecognizedTaxBenefitsIncreaseResultingFromTransferPricingAdjustment_0e82d7b8-64d1-4d0c-b989-ac1915727583" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_IncomeTaxExaminationStatuteOfLimitationForUnderpaymentOfTaxesPeriod_228d5639-6de8-444f-b17e-7dc4a74dedfe" xlink:href="gct-20231231.xsd#gct_IncomeTaxExaminationStatuteOfLimitationForUnderpaymentOfTaxesPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_IncomeTaxDisclosureLineItems_e44d29b1-5a0f-4611-b846-0a3743226b41" xlink:to="loc_gct_IncomeTaxExaminationStatuteOfLimitationForUnderpaymentOfTaxesPeriod_228d5639-6de8-444f-b17e-7dc4a74dedfe" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_IncomeTaxExaminationStatuteOfLimitationForUnderpaymentOfTaxesAboveThresholdLimitPeriod_9627c276-997a-4806-941b-b3834bbd3146" xlink:href="gct-20231231.xsd#gct_IncomeTaxExaminationStatuteOfLimitationForUnderpaymentOfTaxesAboveThresholdLimitPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_IncomeTaxDisclosureLineItems_e44d29b1-5a0f-4611-b846-0a3743226b41" xlink:to="loc_gct_IncomeTaxExaminationStatuteOfLimitationForUnderpaymentOfTaxesAboveThresholdLimitPeriod_9627c276-997a-4806-941b-b3834bbd3146" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_IncomeTaxExaminationStatuteOfLimitationForUnderpaymentOfTaxesAboveThresholdLimit_f083e5c5-4579-430c-ad42-43b7d96a8f26" xlink:href="gct-20231231.xsd#gct_IncomeTaxExaminationStatuteOfLimitationForUnderpaymentOfTaxesAboveThresholdLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_IncomeTaxDisclosureLineItems_e44d29b1-5a0f-4611-b846-0a3743226b41" xlink:to="loc_gct_IncomeTaxExaminationStatuteOfLimitationForUnderpaymentOfTaxesAboveThresholdLimit_f083e5c5-4579-430c-ad42-43b7d96a8f26" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_IncomeTaxExaminationThresholdLimitForTransferPricing_c0b3e990-c6fb-4dbf-af17-d6fcdb03139e" xlink:href="gct-20231231.xsd#gct_IncomeTaxExaminationThresholdLimitForTransferPricing"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_IncomeTaxDisclosureLineItems_e44d29b1-5a0f-4611-b846-0a3743226b41" xlink:to="loc_gct_IncomeTaxExaminationThresholdLimitForTransferPricing_c0b3e990-c6fb-4dbf-af17-d6fcdb03139e" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/IncomeTaxScheduleofthecomponentsofincomebeforeincometaxesDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#IncomeTaxScheduleofthecomponentsofincomebeforeincometaxesDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/IncomeTaxScheduleofthecomponentsofincomebeforeincometaxesDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_gct_ComponentsOfIncomeBeforeIncomeTaxesLineItems_33c0b333-848f-4a32-a24f-d95119648c19" xlink:href="gct-20231231.xsd#gct_ComponentsOfIncomeBeforeIncomeTaxesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ComponentsOfIncomeBeforeIncomeTaxesTable_05a14179-615e-43a4-83db-60906cbdc2a4" xlink:href="gct-20231231.xsd#gct_ComponentsOfIncomeBeforeIncomeTaxesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_gct_ComponentsOfIncomeBeforeIncomeTaxesLineItems_33c0b333-848f-4a32-a24f-d95119648c19" xlink:to="loc_gct_ComponentsOfIncomeBeforeIncomeTaxesTable_05a14179-615e-43a4-83db-60906cbdc2a4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_fc64595d-6da8-4e8b-be1c-15a11841b222" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeTaxAuthorityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_ComponentsOfIncomeBeforeIncomeTaxesTable_05a14179-615e-43a4-83db-60906cbdc2a4" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_fc64595d-6da8-4e8b-be1c-15a11841b222" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_fc64595d-6da8-4e8b-be1c-15a11841b222_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_fc64595d-6da8-4e8b-be1c-15a11841b222" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_fc64595d-6da8-4e8b-be1c-15a11841b222_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_51e4d26f-2931-4157-9885-b2af118e5125" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_fc64595d-6da8-4e8b-be1c-15a11841b222" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_51e4d26f-2931-4157-9885-b2af118e5125" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_HK_6c02e38d-cfef-473c-b5e0-2aae3c387be8" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_HK"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_51e4d26f-2931-4157-9885-b2af118e5125" xlink:to="loc_country_HK_6c02e38d-cfef-473c-b5e0-2aae3c387be8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_CN_d6788f60-8804-40ed-af97-17256ef75ec1" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_CN"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_51e4d26f-2931-4157-9885-b2af118e5125" xlink:to="loc_country_CN_d6788f60-8804-40ed-af97-17256ef75ec1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_90cf8fd8-0ef3-4436-a115-01ff62e29a16" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_51e4d26f-2931-4157-9885-b2af118e5125" xlink:to="loc_country_US_90cf8fd8-0ef3-4436-a115-01ff62e29a16" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_DE_03a07554-0ec5-4cf2-be18-416df9dce6fe" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_DE"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_51e4d26f-2931-4157-9885-b2af118e5125" xlink:to="loc_country_DE_03a07554-0ec5-4cf2-be18-416df9dce6fe" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_OthersMember_b61f5214-55ff-46b8-9f5a-aa62c8a133f9" xlink:href="gct-20231231.xsd#gct_OthersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_51e4d26f-2931-4157-9885-b2af118e5125" xlink:to="loc_gct_OthersMember_b61f5214-55ff-46b8-9f5a-aa62c8a133f9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_c031513a-f428-4040-811f-7d0764fdf521" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ComponentsOfIncomeBeforeIncomeTaxesLineItems_33c0b333-848f-4a32-a24f-d95119648c19" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_c031513a-f428-4040-811f-7d0764fdf521" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/IncomeTaxScheduleofincometaxexpensesDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#IncomeTaxScheduleofincometaxexpensesDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/IncomeTaxScheduleofincometaxexpensesDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_gct_ScheduleOfComponentsOfIncomeTaxExpenseBenefitLineItems_387b54e0-cdb7-4db2-9e94-472f3b14fba7" xlink:href="gct-20231231.xsd#gct_ScheduleOfComponentsOfIncomeTaxExpenseBenefitLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTable_b4e604d5-3503-4c7e-bcea-d648d02b5c8e" xlink:href="gct-20231231.xsd#gct_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_gct_ScheduleOfComponentsOfIncomeTaxExpenseBenefitLineItems_387b54e0-cdb7-4db2-9e94-472f3b14fba7" xlink:to="loc_gct_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTable_b4e604d5-3503-4c7e-bcea-d648d02b5c8e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_e0ee50a4-b8a6-49f0-9c0b-4a041e3af776" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTable_b4e604d5-3503-4c7e-bcea-d648d02b5c8e" xlink:to="loc_srt_StatementGeographicalAxis_e0ee50a4-b8a6-49f0-9c0b-4a041e3af776" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_e0ee50a4-b8a6-49f0-9c0b-4a041e3af776_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_e0ee50a4-b8a6-49f0-9c0b-4a041e3af776" xlink:to="loc_srt_SegmentGeographicalDomain_e0ee50a4-b8a6-49f0-9c0b-4a041e3af776_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_65a963ff-e130-41a8-84fd-dc4a49235a21" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_e0ee50a4-b8a6-49f0-9c0b-4a041e3af776" xlink:to="loc_srt_SegmentGeographicalDomain_65a963ff-e130-41a8-84fd-dc4a49235a21" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_4c3e951e-ad8f-4970-99ca-6fdb86f0e4e6" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_65a963ff-e130-41a8-84fd-dc4a49235a21" xlink:to="loc_country_US_4c3e951e-ad8f-4970-99ca-6fdb86f0e4e6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_CN_444aee43-f5c0-4bf0-b07a-d51c8b4c821b" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_CN"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_65a963ff-e130-41a8-84fd-dc4a49235a21" xlink:to="loc_country_CN_444aee43-f5c0-4bf0-b07a-d51c8b4c821b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_DE_1927fd8f-7465-41db-b39a-d0d582ef9e40" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_DE"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_65a963ff-e130-41a8-84fd-dc4a49235a21" xlink:to="loc_country_DE_1927fd8f-7465-41db-b39a-d0d582ef9e40" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_OthersMember_ecaa016f-ba8b-4317-8ca5-e39b41f44918" xlink:href="gct-20231231.xsd#gct_OthersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_65a963ff-e130-41a8-84fd-dc4a49235a21" xlink:to="loc_gct_OthersMember_ecaa016f-ba8b-4317-8ca5-e39b41f44918" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CurrentIncomeTaxExpenseBenefitContinuingOperationsAbstract_67b6831d-1a3d-4d07-bad4-983bd2f6b1cd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CurrentIncomeTaxExpenseBenefitContinuingOperationsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfComponentsOfIncomeTaxExpenseBenefitLineItems_387b54e0-cdb7-4db2-9e94-472f3b14fba7" xlink:to="loc_us-gaap_CurrentIncomeTaxExpenseBenefitContinuingOperationsAbstract_67b6831d-1a3d-4d07-bad4-983bd2f6b1cd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CurrentIncomeTaxExpenseBenefit_d8b5175c-683b-4282-b781-8737c41ddcbf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CurrentIncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CurrentIncomeTaxExpenseBenefitContinuingOperationsAbstract_67b6831d-1a3d-4d07-bad4-983bd2f6b1cd" xlink:to="loc_us-gaap_CurrentIncomeTaxExpenseBenefit_d8b5175c-683b-4282-b781-8737c41ddcbf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxExpenseBenefitContinuingOperationsAbstract_d81a8243-a207-490e-8d7b-3f76eeb85ef8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredIncomeTaxExpenseBenefitContinuingOperationsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfComponentsOfIncomeTaxExpenseBenefitLineItems_387b54e0-cdb7-4db2-9e94-472f3b14fba7" xlink:to="loc_us-gaap_DeferredIncomeTaxExpenseBenefitContinuingOperationsAbstract_d81a8243-a207-490e-8d7b-3f76eeb85ef8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_e488f26e-c811-4f33-8506-2b3a62f813cd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredIncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredIncomeTaxExpenseBenefitContinuingOperationsAbstract_d81a8243-a207-490e-8d7b-3f76eeb85ef8" xlink:to="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_e488f26e-c811-4f33-8506-2b3a62f813cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_626bb792-3904-433a-9053-e105c5293261" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_ScheduleOfComponentsOfIncomeTaxExpenseBenefitLineItems_387b54e0-cdb7-4db2-9e94-472f3b14fba7" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_626bb792-3904-433a-9053-e105c5293261" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/NetIncomeperOrdinaryShareScheduleoftheBasicandDilutedNetIncomeperOrdinaryShareAdditionalInformationDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#NetIncomeperOrdinaryShareScheduleoftheBasicandDilutedNetIncomeperOrdinaryShareAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/NetIncomeperOrdinaryShareScheduleoftheBasicandDilutedNetIncomeperOrdinaryShareAdditionalInformationDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockLineItems_c6307dac-0f00-4f16-9655-5fe724299d5a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConversionOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockTable_7147e879-53e8-4863-87d1-8dce9fe50b23" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConversionOfStockTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConversionOfStockLineItems_c6307dac-0f00-4f16-9655-5fe724299d5a" xlink:to="loc_us-gaap_ConversionOfStockTable_7147e879-53e8-4863-87d1-8dce9fe50b23" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_d8c79b8e-6b76-47a3-a038-77a370577e03" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConversionOfStockTable_7147e879-53e8-4863-87d1-8dce9fe50b23" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_d8c79b8e-6b76-47a3-a038-77a370577e03" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_d8c79b8e-6b76-47a3-a038-77a370577e03_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_d8c79b8e-6b76-47a3-a038-77a370577e03" xlink:to="loc_us-gaap_RelatedPartyDomain_d8c79b8e-6b76-47a3-a038-77a370577e03_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_f5b3bddc-9273-4336-975b-a8512262a441" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_d8c79b8e-6b76-47a3-a038-77a370577e03" xlink:to="loc_us-gaap_RelatedPartyDomain_f5b3bddc-9273-4336-975b-a8512262a441" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_TrustHoldcosMember_2dcb090c-ceb0-4bda-9a3c-08f28ac30d55" xlink:href="gct-20231231.xsd#gct_TrustHoldcosMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_f5b3bddc-9273-4336-975b-a8512262a441" xlink:to="loc_gct_TrustHoldcosMember_2dcb090c-ceb0-4bda-9a3c-08f28ac30d55" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_6ff3338b-dcea-4c69-bf04-b8beb22628b4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConversionOfStockTable_7147e879-53e8-4863-87d1-8dce9fe50b23" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_6ff3338b-dcea-4c69-bf04-b8beb22628b4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_6ff3338b-dcea-4c69-bf04-b8beb22628b4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_6ff3338b-dcea-4c69-bf04-b8beb22628b4" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_6ff3338b-dcea-4c69-bf04-b8beb22628b4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_87808c2e-d1e4-41ce-949d-5ba39b0bda91" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_6ff3338b-dcea-4c69-bf04-b8beb22628b4" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_87808c2e-d1e4-41ce-949d-5ba39b0bda91" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_6eb6463d-d1a7-4aab-b894-4cb8fb3d2b08" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_87808c2e-d1e4-41ce-949d-5ba39b0bda91" xlink:to="loc_us-gaap_WarrantMember_6eb6463d-d1a7-4aab-b894-4cb8fb3d2b08" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_5a0150f1-7cb0-4167-9b16-38c89c17248f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_87808c2e-d1e4-41ce-949d-5ba39b0bda91" xlink:to="loc_us-gaap_RestrictedStockMember_5a0150f1-7cb0-4167-9b16-38c89c17248f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_9621c622-6fdf-4a14-9976-cede7023ba83" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConversionOfStockTable_7147e879-53e8-4863-87d1-8dce9fe50b23" xlink:to="loc_us-gaap_StatementClassOfStockAxis_9621c622-6fdf-4a14-9976-cede7023ba83" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_9621c622-6fdf-4a14-9976-cede7023ba83_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_9621c622-6fdf-4a14-9976-cede7023ba83" xlink:to="loc_us-gaap_ClassOfStockDomain_9621c622-6fdf-4a14-9976-cede7023ba83_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_60826a60-bedb-45ec-b3ac-ece873873c3b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_9621c622-6fdf-4a14-9976-cede7023ba83" xlink:to="loc_us-gaap_ClassOfStockDomain_60826a60-bedb-45ec-b3ac-ece873873c3b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_SeriesABCDEPreferredStockMember_51eba744-e704-4c08-bce5-79b3937b56f2" xlink:href="gct-20231231.xsd#gct_SeriesABCDEPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_60826a60-bedb-45ec-b3ac-ece873873c3b" xlink:to="loc_gct_SeriesABCDEPreferredStockMember_51eba744-e704-4c08-bce5-79b3937b56f2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_d86be411-977c-4115-a255-9b3518a58e43" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_60826a60-bedb-45ec-b3ac-ece873873c3b" xlink:to="loc_us-gaap_CommonClassAMember_d86be411-977c-4115-a255-9b3518a58e43" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_eb849452-025a-42f8-8456-c8a8467b0678" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConversionOfStockByUniqueDescriptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConversionOfStockTable_7147e879-53e8-4863-87d1-8dce9fe50b23" xlink:to="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_eb849452-025a-42f8-8456-c8a8467b0678" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_eb849452-025a-42f8-8456-c8a8467b0678_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConversionOfStockNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_eb849452-025a-42f8-8456-c8a8467b0678" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_eb849452-025a-42f8-8456-c8a8467b0678_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_8c1b2dda-3451-481b-b3af-08bb2501aae1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConversionOfStockNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_eb849452-025a-42f8-8456-c8a8467b0678" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_8c1b2dda-3451-481b-b3af-08bb2501aae1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ConversionOfTemporaryEquitySeriesEPreferredSharesToClassAOrdinarySharesMember_f951ffd1-0594-480e-9e67-b5b4ec73640b" xlink:href="gct-20231231.xsd#gct_ConversionOfTemporaryEquitySeriesEPreferredSharesToClassAOrdinarySharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_8c1b2dda-3451-481b-b3af-08bb2501aae1" xlink:to="loc_gct_ConversionOfTemporaryEquitySeriesEPreferredSharesToClassAOrdinarySharesMember_f951ffd1-0594-480e-9e67-b5b4ec73640b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesHeldInEmployeeTrustShares_b1300f6b-4e1b-43b1-849f-e1b400e4f70d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesHeldInEmployeeTrustShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_c6307dac-0f00-4f16-9655-5fe724299d5a" xlink:to="loc_us-gaap_CommonStockSharesHeldInEmployeeTrustShares_b1300f6b-4e1b-43b1-849f-e1b400e4f70d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_00339733-1d63-4da2-adca-c200b0253f2d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_c6307dac-0f00-4f16-9655-5fe724299d5a" xlink:to="loc_us-gaap_PreferredStockSharesIssued_00339733-1d63-4da2-adca-c200b0253f2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_7aa1aa8d-d193-4c3d-8067-ba0a07a6c263" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_c6307dac-0f00-4f16-9655-5fe724299d5a" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_7aa1aa8d-d193-4c3d-8067-ba0a07a6c263" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_3ca2bafa-8487-4008-815a-b0230beb6ddf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_c6307dac-0f00-4f16-9655-5fe724299d5a" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_3ca2bafa-8487-4008-815a-b0230beb6ddf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_b554b23b-899b-4937-98f9-529348a154f6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_c6307dac-0f00-4f16-9655-5fe724299d5a" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_b554b23b-899b-4937-98f9-529348a154f6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_5c9fc202-7023-4df4-93fa-81868afedfd5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_c6307dac-0f00-4f16-9655-5fe724299d5a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_5c9fc202-7023-4df4-93fa-81868afedfd5" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/NetIncomeperOrdinaryShareScheduleofDilutiveSecuritiesonNetIncomePerShareDetails" xlink:type="simple" xlink:href="gct-20231231.xsd#NetIncomeperOrdinaryShareScheduleofDilutiveSecuritiesonNetIncomePerShareDetails"/>
  <link:definitionLink xlink:role="http://gig.com/role/NetIncomeperOrdinaryShareScheduleofDilutiveSecuritiesonNetIncomePerShareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDilutedLineItems_323090eb-79f0-4438-bd8e-dc7e730b00ac" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EarningsPerShareDilutedLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEarningsPerShareDilutedByCommonClassTable_e06abebd-b2aa-4462-9036-da1bea6d1456" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfEarningsPerShareDilutedByCommonClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EarningsPerShareDilutedLineItems_323090eb-79f0-4438-bd8e-dc7e730b00ac" xlink:to="loc_us-gaap_ScheduleOfEarningsPerShareDilutedByCommonClassTable_e06abebd-b2aa-4462-9036-da1bea6d1456" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_59ccd6d5-6cfb-4e4e-a666-ab29eba9a14e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEarningsPerShareDilutedByCommonClassTable_e06abebd-b2aa-4462-9036-da1bea6d1456" xlink:to="loc_us-gaap_AwardTypeAxis_59ccd6d5-6cfb-4e4e-a666-ab29eba9a14e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_59ccd6d5-6cfb-4e4e-a666-ab29eba9a14e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_59ccd6d5-6cfb-4e4e-a666-ab29eba9a14e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_59ccd6d5-6cfb-4e4e-a666-ab29eba9a14e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f24bfba7-f433-4174-90b7-f82838d8f0e3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_59ccd6d5-6cfb-4e4e-a666-ab29eba9a14e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f24bfba7-f433-4174-90b7-f82838d8f0e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_0f65adb7-03e9-49e7-ba8b-f5c6a8e88a26" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f24bfba7-f433-4174-90b7-f82838d8f0e3" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_0f65adb7-03e9-49e7-ba8b-f5c6a8e88a26" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_7e3d7cf9-c99c-4da1-a28a-4baad01e66d3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f24bfba7-f433-4174-90b7-f82838d8f0e3" xlink:to="loc_us-gaap_RestrictedStockMember_7e3d7cf9-c99c-4da1-a28a-4baad01e66d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_9337b2a1-96db-4cf6-a4fc-e8e7f7d03c99" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareDilutedLineItems_323090eb-79f0-4438-bd8e-dc7e730b00ac" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_9337b2a1-96db-4cf6-a4fc-e8e7f7d03c99" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/RevenuesScheduleofrevenuesaredisaggregatedbymajorproductsandservicelinesandtimingofrevenuerecognitionDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#RevenuesScheduleofrevenuesaredisaggregatedbymajorproductsandservicelinesandtimingofrevenuerecognitionDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/RevenuesScheduleofrevenuesaredisaggregatedbymajorproductsandservicelinesandtimingofrevenuerecognitionDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_3cd313d2-9142-407f-b1d4-8ac8166f45e5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_aca26481-8d7d-4cf2-9feb-ff90df5f1f5b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_3cd313d2-9142-407f-b1d4-8ac8166f45e5" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_aca26481-8d7d-4cf2-9feb-ff90df5f1f5b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_17af2afd-61b1-4fc7-9bcb-a5cee2439fbf" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_aca26481-8d7d-4cf2-9feb-ff90df5f1f5b" xlink:to="loc_srt_ProductOrServiceAxis_17af2afd-61b1-4fc7-9bcb-a5cee2439fbf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_17af2afd-61b1-4fc7-9bcb-a5cee2439fbf_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_17af2afd-61b1-4fc7-9bcb-a5cee2439fbf" xlink:to="loc_srt_ProductsAndServicesDomain_17af2afd-61b1-4fc7-9bcb-a5cee2439fbf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_441d904c-f172-4922-ac52-f4fecec35600" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_17af2afd-61b1-4fc7-9bcb-a5cee2439fbf" xlink:to="loc_srt_ProductsAndServicesDomain_441d904c-f172-4922-ac52-f4fecec35600" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PlatformCommissionMember_fa07bffa-a839-4cb7-8e74-29f4e0f498fe" xlink:href="gct-20231231.xsd#gct_PlatformCommissionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_441d904c-f172-4922-ac52-f4fecec35600" xlink:to="loc_gct_PlatformCommissionMember_fa07bffa-a839-4cb7-8e74-29f4e0f498fe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_OceanTransportationServiceMember_2515f584-bed2-4c5e-baaf-a96336e4a125" xlink:href="gct-20231231.xsd#gct_OceanTransportationServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_441d904c-f172-4922-ac52-f4fecec35600" xlink:to="loc_gct_OceanTransportationServiceMember_2515f584-bed2-4c5e-baaf-a96336e4a125" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_WarehousingServiceMember_49d79302-40c8-4b24-a6bd-3351839cd5b8" xlink:href="gct-20231231.xsd#gct_WarehousingServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_441d904c-f172-4922-ac52-f4fecec35600" xlink:to="loc_gct_WarehousingServiceMember_49d79302-40c8-4b24-a6bd-3351839cd5b8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_LastmileDeliveryServiceMember_b8aa9d12-19a9-4bb3-a15c-236ece345499" xlink:href="gct-20231231.xsd#gct_LastmileDeliveryServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_441d904c-f172-4922-ac52-f4fecec35600" xlink:to="loc_gct_LastmileDeliveryServiceMember_b8aa9d12-19a9-4bb3-a15c-236ece345499" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PackagingServiceMember_337f587a-ce4a-43a1-a250-5d4e40575feb" xlink:href="gct-20231231.xsd#gct_PackagingServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_441d904c-f172-4922-ac52-f4fecec35600" xlink:to="loc_gct_PackagingServiceMember_337f587a-ce4a-43a1-a250-5d4e40575feb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServiceOtherMember_fa478b29-53ec-4e7d-a119-fb1f545d14d2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ServiceOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_441d904c-f172-4922-ac52-f4fecec35600" xlink:to="loc_us-gaap_ServiceOtherMember_fa478b29-53ec-4e7d-a119-fb1f545d14d2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServiceMember_dc8a64bd-a517-4fd7-96e7-ad1d98dbf9af" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_441d904c-f172-4922-ac52-f4fecec35600" xlink:to="loc_us-gaap_ServiceMember_dc8a64bd-a517-4fd7-96e7-ad1d98dbf9af" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_05cdb7b2-76ff-4d35-bc3d-74fd3caec546" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_441d904c-f172-4922-ac52-f4fecec35600" xlink:to="loc_us-gaap_ProductMember_05cdb7b2-76ff-4d35-bc3d-74fd3caec546" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerSalesChannelAxis_8d87bb0b-a237-4e09-956f-e0a70f370d76" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ContractWithCustomerSalesChannelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_aca26481-8d7d-4cf2-9feb-ff90df5f1f5b" xlink:to="loc_us-gaap_ContractWithCustomerSalesChannelAxis_8d87bb0b-a237-4e09-956f-e0a70f370d76" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerSalesChannelDomain_8d87bb0b-a237-4e09-956f-e0a70f370d76_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ContractWithCustomerSalesChannelDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ContractWithCustomerSalesChannelAxis_8d87bb0b-a237-4e09-956f-e0a70f370d76" xlink:to="loc_us-gaap_ContractWithCustomerSalesChannelDomain_8d87bb0b-a237-4e09-956f-e0a70f370d76_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerSalesChannelDomain_2fb3c22f-58ad-4e14-9dc7-be5a8902edd1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ContractWithCustomerSalesChannelDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ContractWithCustomerSalesChannelAxis_8d87bb0b-a237-4e09-956f-e0a70f370d76" xlink:to="loc_us-gaap_ContractWithCustomerSalesChannelDomain_2fb3c22f-58ad-4e14-9dc7-be5a8902edd1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_OffPlatformEcommerceMember_83cf2c2d-f4dd-4682-a68a-ac364c2628e9" xlink:href="gct-20231231.xsd#gct_OffPlatformEcommerceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerSalesChannelDomain_2fb3c22f-58ad-4e14-9dc7-be5a8902edd1" xlink:to="loc_gct_OffPlatformEcommerceMember_83cf2c2d-f4dd-4682-a68a-ac364c2628e9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_Gigacloud1pMember_d288918b-014b-4c36-bc46-37b6973c2564" xlink:href="gct-20231231.xsd#gct_Gigacloud1pMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerSalesChannelDomain_2fb3c22f-58ad-4e14-9dc7-be5a8902edd1" xlink:to="loc_gct_Gigacloud1pMember_d288918b-014b-4c36-bc46-37b6973c2564" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_OthersMember_4ebfafa7-4c4d-4a3d-aecb-62131a3ffacb" xlink:href="gct-20231231.xsd#gct_OthersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerSalesChannelDomain_2fb3c22f-58ad-4e14-9dc7-be5a8902edd1" xlink:to="loc_gct_OthersMember_4ebfafa7-4c4d-4a3d-aecb-62131a3ffacb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_0fd11402-f6ee-44df-aef8-018c94d84c34" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_aca26481-8d7d-4cf2-9feb-ff90df5f1f5b" xlink:to="loc_srt_MajorCustomersAxis_0fd11402-f6ee-44df-aef8-018c94d84c34" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_0fd11402-f6ee-44df-aef8-018c94d84c34_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_0fd11402-f6ee-44df-aef8-018c94d84c34" xlink:to="loc_srt_NameOfMajorCustomerDomain_0fd11402-f6ee-44df-aef8-018c94d84c34_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_042ec513-78e3-4a8f-928d-cc1cb9c6cc55" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_0fd11402-f6ee-44df-aef8-018c94d84c34" xlink:to="loc_srt_NameOfMajorCustomerDomain_042ec513-78e3-4a8f-928d-cc1cb9c6cc55" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ProductSalesToBMember_958be842-784d-49ba-bcae-0072b74895b4" xlink:href="gct-20231231.xsd#gct_ProductSalesToBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_042ec513-78e3-4a8f-928d-cc1cb9c6cc55" xlink:to="loc_gct_ProductSalesToBMember_958be842-784d-49ba-bcae-0072b74895b4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ProductSalesToCMember_be334707-1a1a-47e2-96a9-9915878f4e92" xlink:href="gct-20231231.xsd#gct_ProductSalesToCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_042ec513-78e3-4a8f-928d-cc1cb9c6cc55" xlink:to="loc_gct_ProductSalesToCMember_be334707-1a1a-47e2-96a9-9915878f4e92" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_5d153aa2-1c8d-45aa-b8e5-46db8fa0bd61" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TimingOfTransferOfGoodOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_aca26481-8d7d-4cf2-9feb-ff90df5f1f5b" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_5d153aa2-1c8d-45aa-b8e5-46db8fa0bd61" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_5d153aa2-1c8d-45aa-b8e5-46db8fa0bd61_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TimingOfTransferOfGoodOrServiceDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_5d153aa2-1c8d-45aa-b8e5-46db8fa0bd61" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_5d153aa2-1c8d-45aa-b8e5-46db8fa0bd61_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_c7e17161-eea9-486b-9c13-0798c12447e8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TimingOfTransferOfGoodOrServiceDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_5d153aa2-1c8d-45aa-b8e5-46db8fa0bd61" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_c7e17161-eea9-486b-9c13-0798c12447e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransferredOverTimeMember_7c23309d-06cb-4b6a-b784-880d0cfab354" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TransferredOverTimeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_c7e17161-eea9-486b-9c13-0798c12447e8" xlink:to="loc_us-gaap_TransferredOverTimeMember_7c23309d-06cb-4b6a-b784-880d0cfab354" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransferredAtPointInTimeMember_21625061-8d1e-44ab-8b3f-56b1df4c3a61" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TransferredAtPointInTimeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_c7e17161-eea9-486b-9c13-0798c12447e8" xlink:to="loc_us-gaap_TransferredAtPointInTimeMember_21625061-8d1e-44ab-8b3f-56b1df4c3a61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_6c0c79c5-965a-4187-991c-fbf9231d6823" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_3cd313d2-9142-407f-b1d4-8ac8166f45e5" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_6c0c79c5-965a-4187-991c-fbf9231d6823" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_80f83f3c-552c-47ea-858a-3071d764a6c7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_3cd313d2-9142-407f-b1d4-8ac8166f45e5" xlink:to="loc_us-gaap_Revenues_80f83f3c-552c-47ea-858a-3071d764a6c7" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/RestrictedNetAssetsAdditionalInformationDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#RestrictedNetAssetsAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/RestrictedNetAssetsAdditionalInformationDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_gct_RestrictedNetAssetsLineItems_65d33cab-6736-49ee-b98c-3c15d436a601" xlink:href="gct-20231231.xsd#gct_RestrictedNetAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_RestrictedNetAssetsTable_07662d76-6e72-405d-b864-d5cacf2cab90" xlink:href="gct-20231231.xsd#gct_RestrictedNetAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_gct_RestrictedNetAssetsLineItems_65d33cab-6736-49ee-b98c-3c15d436a601" xlink:to="loc_gct_RestrictedNetAssetsTable_07662d76-6e72-405d-b864-d5cacf2cab90" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_fd693ec6-3500-41da-9357-d03308752603" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gct_RestrictedNetAssetsTable_07662d76-6e72-405d-b864-d5cacf2cab90" xlink:to="loc_srt_StatementGeographicalAxis_fd693ec6-3500-41da-9357-d03308752603" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_fd693ec6-3500-41da-9357-d03308752603_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_fd693ec6-3500-41da-9357-d03308752603" xlink:to="loc_srt_SegmentGeographicalDomain_fd693ec6-3500-41da-9357-d03308752603_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_321c2e90-be15-4bbd-91b5-16d522be450a" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_fd693ec6-3500-41da-9357-d03308752603" xlink:to="loc_srt_SegmentGeographicalDomain_321c2e90-be15-4bbd-91b5-16d522be450a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_CN_7ee3b4b3-6d54-4050-a3bb-62710ee4bbfd" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_CN"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_321c2e90-be15-4bbd-91b5-16d522be450a" xlink:to="loc_country_CN_7ee3b4b3-6d54-4050-a3bb-62710ee4bbfd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_MinimumPercentageOfAllocationOfAnnualafterTaxprofitsToTheGeneralReserveFund_1d3f0498-a9c6-49ce-a0ca-06261db4fae4" xlink:href="gct-20231231.xsd#gct_MinimumPercentageOfAllocationOfAnnualafterTaxprofitsToTheGeneralReserveFund"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_RestrictedNetAssetsLineItems_65d33cab-6736-49ee-b98c-3c15d436a601" xlink:to="loc_gct_MinimumPercentageOfAllocationOfAnnualafterTaxprofitsToTheGeneralReserveFund_1d3f0498-a9c6-49ce-a0ca-06261db4fae4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ThresholdPercentageOfGeneralReserveFundToRegisteredCapital_48089654-927d-412f-9566-c6f8bdf2ccc0" xlink:href="gct-20231231.xsd#gct_ThresholdPercentageOfGeneralReserveFundToRegisteredCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_RestrictedNetAssetsLineItems_65d33cab-6736-49ee-b98c-3c15d436a601" xlink:to="loc_gct_ThresholdPercentageOfGeneralReserveFundToRegisteredCapital_48089654-927d-412f-9566-c6f8bdf2ccc0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_MinimumPercentageOfAllocationOfAnnualafterTaxprofitsToTheStatutorySurplusFund_95979381-4a8c-42c0-9241-6703a3674370" xlink:href="gct-20231231.xsd#gct_MinimumPercentageOfAllocationOfAnnualafterTaxprofitsToTheStatutorySurplusFund"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_RestrictedNetAssetsLineItems_65d33cab-6736-49ee-b98c-3c15d436a601" xlink:to="loc_gct_MinimumPercentageOfAllocationOfAnnualafterTaxprofitsToTheStatutorySurplusFund_95979381-4a8c-42c0-9241-6703a3674370" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ThresholdPercentageOfStatutorySurplusFundToRegisteredCapital_7440e84b-9a16-4e16-96de-abc95fa80bf1" xlink:href="gct-20231231.xsd#gct_ThresholdPercentageOfStatutorySurplusFundToRegisteredCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_RestrictedNetAssetsLineItems_65d33cab-6736-49ee-b98c-3c15d436a601" xlink:to="loc_gct_ThresholdPercentageOfStatutorySurplusFundToRegisteredCapital_7440e84b-9a16-4e16-96de-abc95fa80bf1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_PercentageOfAnnualAppropriations_a48db72e-a0cc-4f4a-9380-359e38e4d1c9" xlink:href="gct-20231231.xsd#gct_PercentageOfAnnualAppropriations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_RestrictedNetAssetsLineItems_65d33cab-6736-49ee-b98c-3c15d436a601" xlink:to="loc_gct_PercentageOfAnnualAppropriations_a48db72e-a0cc-4f4a-9380-359e38e4d1c9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ThresholdPercentageUnderRule504C_ecf336b1-caa3-47f1-b2ee-89787fafd841" xlink:href="gct-20231231.xsd#gct_ThresholdPercentageUnderRule504C"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gct_RestrictedNetAssetsLineItems_65d33cab-6736-49ee-b98c-3c15d436a601" xlink:to="loc_gct_ThresholdPercentageUnderRule504C_ecf336b1-caa3-47f1-b2ee-89787fafd841" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://gig.com/role/SubsequentEventsAdditionalInformationDetail" xlink:type="simple" xlink:href="gct-20231231.xsd#SubsequentEventsAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://gig.com/role/SubsequentEventsAdditionalInformationDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_aa5d9745-51d5-4f72-8a5d-e553e483a4f3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_dd675282-a295-4d52-ad12-20d4f03b76f6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_aa5d9745-51d5-4f72-8a5d-e553e483a4f3" xlink:to="loc_us-gaap_SubsequentEventTable_dd675282-a295-4d52-ad12-20d4f03b76f6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_909ff13f-b64b-449c-964b-9b404078e8ed" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_dd675282-a295-4d52-ad12-20d4f03b76f6" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_909ff13f-b64b-449c-964b-9b404078e8ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_909ff13f-b64b-449c-964b-9b404078e8ed_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_909ff13f-b64b-449c-964b-9b404078e8ed" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_909ff13f-b64b-449c-964b-9b404078e8ed_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_0199fc6b-9096-4e3c-9301-b3b07a5e3170" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_909ff13f-b64b-449c-964b-9b404078e8ed" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_0199fc6b-9096-4e3c-9301-b3b07a5e3170" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_B.T.MTravelAndTradingLtdComharborLimitedBrihomeLimitedAndDecobusHandelGMBHMember_09db5200-41ce-499a-88d0-1a05fbad024b" xlink:href="gct-20231231.xsd#gct_B.T.MTravelAndTradingLtdComharborLimitedBrihomeLimitedAndDecobusHandelGMBHMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_0199fc6b-9096-4e3c-9301-b3b07a5e3170" xlink:to="loc_gct_B.T.MTravelAndTradingLtdComharborLimitedBrihomeLimitedAndDecobusHandelGMBHMember_09db5200-41ce-499a-88d0-1a05fbad024b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_1da3978d-49ad-4a84-9ef2-40561d6fc004" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_dd675282-a295-4d52-ad12-20d4f03b76f6" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_1da3978d-49ad-4a84-9ef2-40561d6fc004" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_1da3978d-49ad-4a84-9ef2-40561d6fc004_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_1da3978d-49ad-4a84-9ef2-40561d6fc004" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_1da3978d-49ad-4a84-9ef2-40561d6fc004_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_0c8a0869-2f50-42a9-ac6c-404a376ba3cd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_1da3978d-49ad-4a84-9ef2-40561d6fc004" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_0c8a0869-2f50-42a9-ac6c-404a376ba3cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_b892bea2-07b5-42eb-8c64-7b446d970e8b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_0c8a0869-2f50-42a9-ac6c-404a376ba3cd" xlink:to="loc_us-gaap_SubsequentEventMember_b892bea2-07b5-42eb-8c64-7b446d970e8b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_f5974b2f-0605-4f09-b11c-c710e18ccde4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_dd675282-a295-4d52-ad12-20d4f03b76f6" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_f5974b2f-0605-4f09-b11c-c710e18ccde4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_f5974b2f-0605-4f09-b11c-c710e18ccde4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_f5974b2f-0605-4f09-b11c-c710e18ccde4" xlink:to="loc_us-gaap_RelatedPartyDomain_f5974b2f-0605-4f09-b11c-c710e18ccde4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_ce96c357-2e24-4304-8a78-68466a3f5925" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_f5974b2f-0605-4f09-b11c-c710e18ccde4" xlink:to="loc_us-gaap_RelatedPartyDomain_ce96c357-2e24-4304-8a78-68466a3f5925" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_UnderwriterMember_b7127e58-e194-41b7-9ea6-572860b090de" xlink:href="gct-20231231.xsd#gct_UnderwriterMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_ce96c357-2e24-4304-8a78-68466a3f5925" xlink:to="loc_gct_UnderwriterMember_b7127e58-e194-41b7-9ea6-572860b090de" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_6fc10317-58b5-4549-b12e-43ae9727ad00" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_dd675282-a295-4d52-ad12-20d4f03b76f6" xlink:to="loc_us-gaap_StatementClassOfStockAxis_6fc10317-58b5-4549-b12e-43ae9727ad00" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_6fc10317-58b5-4549-b12e-43ae9727ad00_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_6fc10317-58b5-4549-b12e-43ae9727ad00" xlink:to="loc_us-gaap_ClassOfStockDomain_6fc10317-58b5-4549-b12e-43ae9727ad00_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_a98ef073-5bda-41f5-a608-e6af4bf4182b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_6fc10317-58b5-4549-b12e-43ae9727ad00" xlink:to="loc_us-gaap_ClassOfStockDomain_a98ef073-5bda-41f5-a608-e6af4bf4182b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_3d286375-7e0f-4060-83e9-e8d9da4fd28b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_a98ef073-5bda-41f5-a608-e6af4bf4182b" xlink:to="loc_us-gaap_CommonClassAMember_3d286375-7e0f-4060-83e9-e8d9da4fd28b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_NumberOfVIEsAgreementsTerminated_be51f755-e25f-4c5e-a717-5e0670eaf201" xlink:href="gct-20231231.xsd#gct_NumberOfVIEsAgreementsTerminated"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_aa5d9745-51d5-4f72-8a5d-e553e483a4f3" xlink:to="loc_gct_NumberOfVIEsAgreementsTerminated_be51f755-e25f-4c5e-a717-5e0670eaf201" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_e8be0b26-3854-467e-bf4c-e94a53bfd26a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_aa5d9745-51d5-4f72-8a5d-e553e483a4f3" xlink:to="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_e8be0b26-3854-467e-bf4c-e94a53bfd26a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_3246b667-1488-4288-8969-e7a675a7c637" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_aa5d9745-51d5-4f72-8a5d-e553e483a4f3" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_3246b667-1488-4288-8969-e7a675a7c637" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_6d749227-5deb-4351-b923-22175ac37304" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_aa5d9745-51d5-4f72-8a5d-e553e483a4f3" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_6d749227-5deb-4351-b923-22175ac37304" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_WarehousesSufferedDamages_f3887487-3530-4db0-ac79-aae2cdb67319" xlink:href="gct-20231231.xsd#gct_WarehousesSufferedDamages"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_aa5d9745-51d5-4f72-8a5d-e553e483a4f3" xlink:to="loc_gct_WarehousesSufferedDamages_f3887487-3530-4db0-ac79-aae2cdb67319" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryWriteDown_d053a7ab-8cba-45d0-be5d-a546e14687be" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InventoryWriteDown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_aa5d9745-51d5-4f72-8a5d-e553e483a4f3" xlink:to="loc_us-gaap_InventoryWriteDown_d053a7ab-8cba-45d0-be5d-a546e14687be" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_TotalGroupWarehousesInJapan_7220dfad-c94c-4e2e-b546-460e1544cc60" xlink:href="gct-20231231.xsd#gct_TotalGroupWarehousesInJapan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_aa5d9745-51d5-4f72-8a5d-e553e483a4f3" xlink:to="loc_gct_TotalGroupWarehousesInJapan_7220dfad-c94c-4e2e-b546-460e1544cc60" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_NumberOfWarehouseUtilizedToMinimizeDisruptions_befc82fc-a1de-48dc-915e-da9509f6613c" xlink:href="gct-20231231.xsd#gct_NumberOfWarehouseUtilizedToMinimizeDisruptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_aa5d9745-51d5-4f72-8a5d-e553e483a4f3" xlink:to="loc_gct_NumberOfWarehouseUtilizedToMinimizeDisruptions_befc82fc-a1de-48dc-915e-da9509f6613c" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-roles-2023.xsd#eedm"/>
  <link:definitionLink xlink:role="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_AccruedLiabilitiesAndOtherCurrentLiabilities_10f53c08-a9a1-44fd-9343-01ae81e15868" xlink:href="gct-20231231.xsd#gct_AccruedLiabilitiesAndOtherCurrentLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract" xlink:to="loc_gct_AccruedLiabilitiesAndOtherCurrentLiabilities_10f53c08-a9a1-44fd-9343-01ae81e15868" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/TradingArrangementsOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2023/ecd-2023.xsd#TradingArrangmentsOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/role/TradingArrangementsOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ecd_AllTradingArrangementsMember" xlink:href="https://xbrl.sec.gov/ecd/2023/ecd-2023.xsd#ecd_AllTradingArrangementsMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ChiefExecutiveOfficerTradingAgreementClassAOrdinarySharesMember_bd06b8ce-6132-40d6-b9ad-d902fd0c78c5" xlink:href="gct-20231231.xsd#gct_ChiefExecutiveOfficerTradingAgreementClassAOrdinarySharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllTradingArrangementsMember" xlink:to="loc_gct_ChiefExecutiveOfficerTradingAgreementClassAOrdinarySharesMember_bd06b8ce-6132-40d6-b9ad-d902fd0c78c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_ChiefExecutiveOfficerTradingAgreementClassBOrdinarySharesMember_e461fd43-5427-41e2-9cab-bbd531337b11" xlink:href="gct-20231231.xsd#gct_ChiefExecutiveOfficerTradingAgreementClassBOrdinarySharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllTradingArrangementsMember" xlink:to="loc_gct_ChiefExecutiveOfficerTradingAgreementClassBOrdinarySharesMember_e461fd43-5427-41e2-9cab-bbd531337b11" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_OtherDirectorOrOfficerTradingAgreementMember_eb90e699-cea3-4a50-af52-74c7f585e511" xlink:href="gct-20231231.xsd#gct_OtherDirectorOrOfficerTradingAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllTradingArrangementsMember" xlink:to="loc_gct_OtherDirectorOrOfficerTradingAgreementMember_eb90e699-cea3-4a50-af52-74c7f585e511" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/AwardTypeOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2023/ecd-2023.xsd#AwardTypeOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/AwardTypeOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaap_RestrictedStockMember" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2023/ecd-2023.xsd#IndividualsOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ecd_AllIndividualsMember" xlink:href="https://xbrl.sec.gov/ecd/2023/ecd-2023.xsd#ecd_AllIndividualsMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_gct_Mr.larryLeiWuMember_c2c33232-1b62-440e-86f0-e09da0ca897d" xlink:href="gct-20231231.xsd#gct_Mr.larryLeiWuMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_gct_Mr.larryLeiWuMember_c2c33232-1b62-440e-86f0-e09da0ca897d" xlink:type="arc" order="2"/>
  </link:definitionLink>
</link:linkbase>
