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<!-- DFIN ActiveDisclosure(SM) XBRL Schema Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date      : 2021-03-05T20:03:18.8363106+00:00 -->
<!-- Version            : 5.0.1.571 -->
<!-- Package ID         : 20fad6e94d894dc69b4010568f54acc9 -->
<!-- Copyright (c) 2021 Donnelley Financial Solutions, Inc. All Rights Reserved. -->
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  <xsd:element id="gray_SeriesAConvertiblePreferredStockMember" name="SeriesAConvertiblePreferredStockMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="gray_SeriesATwoConvertiblePreferredStockMember" name="SeriesATwoConvertiblePreferredStockMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="gray_SeriesBConvertiblePreferredStockMember" name="SeriesBConvertiblePreferredStockMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="gray_TemporaryEquityStockIssuedAdditionalDuringPeriodSharesNewIssues" name="TemporaryEquityStockIssuedAdditionalDuringPeriodSharesNewIssues" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="gray_TemporaryEquityPricePerShare" name="TemporaryEquityPricePerShare" type="num:perShareItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="gray_TemporaryEquityOptionToPurchaseAdditionalSharesPeriodAfterNotified" name="TemporaryEquityOptionToPurchaseAdditionalSharesPeriodAfterNotified" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="gray_FairValueOfPreferredStockTrancheObligation" name="FairValueOfPreferredStockTrancheObligation" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="gray_LiabilitiesCurrentMember" name="LiabilitiesCurrentMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="gray_SeriesCPreferredSeriesBPreferredAndSeriesATwoPreferredMember" name="SeriesCPreferredSeriesBPreferredAndSeriesATwoPreferredMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="gray_SeriesATwoPreferredSeriesBPreferredAndSeriesCPreferredMember" name="SeriesATwoPreferredSeriesBPreferredAndSeriesCPreferredMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="gray_DividendsRightsAmountPerShareOnOutstandingSharePayable" name="DividendsRightsAmountPerShareOnOutstandingSharePayable" type="num:perShareItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="gray_PercentageOfAggregateNumberOfSharesOfCommonStockOutstandingOnLastDayOfPrecedingYearAddedToPlan" name="PercentageOfAggregateNumberOfSharesOfCommonStockOutstandingOnLastDayOfPrecedingYearAddedToPlan" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="gray_TwoThousandAndTwentyEquityIncentivePlanMember" name="TwoThousandAndTwentyEquityIncentivePlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="gray_TwoThousandAndTwentyEmployeeStockPurchasePlanMember" name="TwoThousandAndTwentyEmployeeStockPurchasePlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="gray_EffectiveIncomeTaxRateReconciliationMarkToMarketGainOrLoss" name="EffectiveIncomeTaxRateReconciliationMarkToMarketGainOrLoss" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="gray_IncomeTaxesAbstract" name="IncomeTaxesAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="gray_DeferredIncomeTaxLiabilitiesDepreciation" name="DeferredIncomeTaxLiabilitiesDepreciation" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="gray_IncomeTaxesLineItems" name="IncomeTaxesLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="gray_IncomeTaxesTable" name="IncomeTaxesTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="gray_OperatingLossCarryforwardsExpirationBeginningYear" name="OperatingLossCarryforwardsExpirationBeginningYear" type="xbrli:gYearItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="gray_TaxCreditCarryforwardExpirationBeginningYear" name="TaxCreditCarryforwardExpirationBeginningYear" type="xbrli:gYearItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
</xsd:schema>
