<SEC-DOCUMENT>0001209191-19-045418.txt : 20190809
<SEC-HEADER>0001209191-19-045418.hdr.sgml : 20190809
<ACCEPTANCE-DATETIME>20190809191042
ACCESSION NUMBER:		0001209191-19-045418
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20190807
FILED AS OF DATE:		20190809
DATE AS OF CHANGE:		20190809

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Lares Adriel G
		CENTRAL INDEX KEY:			0001416050

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-38897
		FILM NUMBER:		191014150

	MAIL ADDRESS:	
		STREET 1:		C/O YUME, INC.
		STREET 2:		1204 MIDDLEFIELD ROAD
		CITY:			REDWOOD CITY
		STATE:			CA
		ZIP:			94063

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Fastly, Inc.
		CENTRAL INDEX KEY:			0001517413
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-PREPACKAGED SOFTWARE [7372]
		IRS NUMBER:				275411834
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		475 BRANNAN
		STREET 2:		SUITE 300
		CITY:			SAN FRANCISCO
		STATE:			CA
		ZIP:			94107
		BUSINESS PHONE:		415-525-3481

	MAIL ADDRESS:	
		STREET 1:		475 BRANNAN
		STREET 2:		SUITE 300
		CITY:			SAN FRANCISCO
		STATE:			CA
		ZIP:			94107

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	Skycache, Inc.(DE)
		DATE OF NAME CHANGE:	20110405
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>doc4.xml
<DESCRIPTION>FORM 4 SUBMISSION
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2019-08-07</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001517413</issuerCik>
        <issuerName>Fastly, Inc.</issuerName>
        <issuerTradingSymbol>FSLY</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001416050</rptOwnerCik>
            <rptOwnerName>Lares Adriel G</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O FASTLY, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>475 BRANNAN STREET, SUITE 300</rptOwnerStreet2>
            <rptOwnerCity>SAN FRANCISCO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94107</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chief Financial Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Class A Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2019-08-07</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>69897</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>69897</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">The shares are represented by restricted stock units (RSUs). Each RSU represents a contingent right to receive one share of the Issuer's Class A Common Stock upon settlement.  1/4th of the RSUs will vest on August 15, 2020 and 1/16th of the RSUs will vest quarterly thereafter, subject to the Reporting Person's continued service with the Issuer through each applicable vesting date.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Seth Gottlieb, Attorney-in-Fact for Adriel G. Lares</signatureName>
        <signatureDate>2019-08-09</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
