<SEC-DOCUMENT>0001274737-21-000076.txt : 20210621
<SEC-HEADER>0001274737-21-000076.hdr.sgml : 20210621
<ACCEPTANCE-DATETIME>20210621083903
ACCESSION NUMBER:		0001274737-21-000076
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20210617
FILED AS OF DATE:		20210621
DATE AS OF CHANGE:		20210621

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Robertson Bruce C
		CENTRAL INDEX KEY:			0001289625

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-39049
		FILM NUMBER:		211027589

	MAIL ADDRESS:	
		STREET 1:		7600 WISCONSIN AVENUE
		STREET 2:		SUITE 700
		CITY:			BETHESDA
		STATE:			MD
		ZIP:			20814

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			EXAGEN INC.
		CENTRAL INDEX KEY:			0001274737
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-MEDICAL LABORATORIES [8071]
		IRS NUMBER:				000000000
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		1261 LIBERTY WAY
		CITY:			VISTA
		STATE:			CA
		ZIP:			92081
		BUSINESS PHONE:		(760) 560-1501

	MAIL ADDRESS:	
		STREET 1:		1261 LIBERTY WAY
		CITY:			VISTA
		STATE:			CA
		ZIP:			92081

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	EXAGEN DIAGNOSTICS INC
		DATE OF NAME CHANGE:	20031230
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>wf-form4_162427913125759.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2021-06-17</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001274737</issuerCik>
        <issuerName>EXAGEN INC.</issuerName>
        <issuerTradingSymbol>XGN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001289625</rptOwnerCik>
            <rptOwnerName>Robertson Bruce C</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1450 BRICKELL AVENUE, 31ST FLOOR</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>MIAMI</rptOwnerCity>
            <rptOwnerState>FL</rptOwnerState>
            <rptOwnerZipCode>33131</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option(right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>16.41</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2021-06-17</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>9000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2031-06-16</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>9000.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>9000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The entire number of shares subject to this option becomes fully vested and exercisable on the first to occur of (a) the first anniversary of the grant date or (b) the next occurring annual meeting of the Issuer's stockholders, subject to the Reporting Person's continued service on the board of directors of the Issuer through such vesting date.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Bruce Robertson</signatureName>
        <signatureDate>2021-06-21</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
