<SEC-DOCUMENT>0001944544-25-000014.txt : 20250903
<SEC-HEADER>0001944544-25-000014.hdr.sgml : 20250903
<ACCEPTANCE-DATETIME>20250903170637
ACCESSION NUMBER:		0001944544-25-000014
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20250903
FILED AS OF DATE:		20250903
DATE AS OF CHANGE:		20250903

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Fuller Mark C
		CENTRAL INDEX KEY:			0001944544
		ORGANIZATION NAME:           	

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-41526
		FILM NUMBER:		251290850

	MAIL ADDRESS:	
		STREET 1:		9722 MEYER POINT DRIVE
		CITY:			POTOMAC
		STATE:			MD
		ZIP:			20854

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Castellum, Inc.
		CENTRAL INDEX KEY:			0001877939
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-MANAGEMENT CONSULTING SERVICES [8742]
		ORGANIZATION NAME:           	07 Trade & Services
		EIN:				274079982
		STATE OF INCORPORATION:			NV
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		1934 OLD GALLOWS ROAD
		STREET 2:		SUITE 350
		CITY:			VIENNA
		STATE:			VA
		ZIP:			22182
		BUSINESS PHONE:		(703) 752-6157

	MAIL ADDRESS:	
		STREET 1:		1934 OLD GALLOWS ROAD
		STREET 2:		SUITE 350
		CITY:			VIENNA
		STATE:			VA
		ZIP:			22182
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>wk-form4_1756933593.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2025-09-03</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0001877939</issuerCik>
        <issuerName>Castellum, Inc.</issuerName>
        <issuerTradingSymbol>CTM</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001944544</rptOwnerCik>
            <rptOwnerName>Fuller Mark C</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1934 OLD GALLOWS ROAD</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 350</rptOwnerStreet2>
            <rptOwnerCity>VIENNA</rptOwnerCity>
            <rptOwnerState>VA</rptOwnerState>
            <rptOwnerZipCode>22182</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>Former Officer and Affiliate</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2025-09-03</value>
            </transactionDate>
            <deemedExecutionDate>
                <value>2025-09-03</value>
            </deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>500000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>1.12</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>6113659</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Includes (a) 6,047,519 common shares held by The Mark Chappelle Fuller Revocable Trust, Mark Fuller, TTEE, (b) 50,000 common shares held by Janice Lynn Dudley Revocable Trust, Janice Lynn Dudley TTEE,  and (c) 16,140 common shares held by Mark Fuller.</footnote>
        <footnote id="F2">Effective May 28, 2025, Mr. Fuller ceased to be a member of the Company's board of directors.</footnote>
        <footnote id="F3">Effective June 12, 2025, Mr. Fuller ceased to be an affiliate of the Company.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Mark C. Fuller</signatureName>
        <signatureDate>2025-09-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
