<SEC-DOCUMENT>0000950170-25-016469.txt : 20250207
<SEC-HEADER>0000950170-25-016469.hdr.sgml : 20250207
<ACCEPTANCE-DATETIME>20250207173101
ACCESSION NUMBER:		0000950170-25-016469
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		2
CONFORMED PERIOD OF REPORT:	20250206
FILED AS OF DATE:		20250207
DATE AS OF CHANGE:		20250207

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			GRAY MICHAEL
		CENTRAL INDEX KEY:			0001271411
		ORGANIZATION NAME:           	

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-42366
		FILM NUMBER:		25602996

	MAIL ADDRESS:	
		STREET 1:		C/O CURIS INC
		STREET 2:		4 MAGUIRE ROAD
		CITY:			LEXINGTON
		STATE:			MA
		ZIP:			02421

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Upstream Bio, Inc.
		CENTRAL INDEX KEY:			0002022626
		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]
		ORGANIZATION NAME:           	03 Life Sciences
		IRS NUMBER:				000000000
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		890 WINTER STREET, SUITE 200
		CITY:			WALTHAM
		STATE:			MA
		ZIP:			02451
		BUSINESS PHONE:		781-208-2466

	MAIL ADDRESS:	
		STREET 1:		890 WINTER STREET, SUITE 200
		CITY:			WALTHAM
		STATE:			MA
		ZIP:			02451
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>ownership.xml
<DESCRIPTION>4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2025-02-06</periodOfReport>

    <issuer>
        <issuerCik>0002022626</issuerCik>
        <issuerName>Upstream Bio, Inc.</issuerName>
        <issuerTradingSymbol>UPB</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001271411</rptOwnerCik>
            <rptOwnerName>GRAY MICHAEL</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>UPSTREAM BIO, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>890 WINTER STREET, SUITE 200</rptOwnerStreet2>
            <rptOwnerCity>WALTHAM</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02451</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>false</isDirector>
            <isOfficer>true</isOfficer>
            <isTenPercentOwner>false</isTenPercentOwner>
            <isOther>false</isOther>
            <officerTitle>CFO and COO</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>false</aff10b5One>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>8.53</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2025-02-06</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>false</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>195000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2035-02-05</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>195000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>195000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The shares underlying this option shall vest in forty-eight equal monthly installments following February 6, 2025, subject to the Reporting Person's continued service on each such vesting date.</footnote>
    </footnotes>

    <remarks>Exhibit 24.2 - Substitute Power of Attorney</remarks>

    <ownerSignature>
        <signatureName>/s/ Allison Ambrose, Attorney-in-Fact</signatureName>
        <signatureDate>2025-02-07</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
<DOCUMENT>
<TYPE>EX-24.2
<SEQUENCE>2
<FILENAME>ck0002022626-ex24_2.htm
<DESCRIPTION>EX-24.2
<TEXT>
<html>
 <head>
  <title>EX-24.2</title>
 </head>
 <body style="margin: auto!important;padding: 8px;">
  <div style="padding-top:0.5in;z-index:-3;min-height:1in;position:relative;box-sizing:border-box;"><p style="font-size:10pt;margin-top:0;font-family:Times New Roman;margin-bottom:0;text-align:left;"><font style="white-space:pre-wrap;font-size:12pt;font-family:Times New Roman;font-kerning:none;min-width:fit-content;">&#160;</font></p></div>
  <p style="font-size:10pt;margin-top:0;font-family:Times New Roman;margin-bottom:0;text-align:left;"><font style="color:#000000;white-space:pre-wrap;font-size:12pt;font-family:Times New Roman;font-kerning:none;min-width:fit-content;">SUBSTITUTE POWER OF ATTORNEY</font><font style="color:#000000;white-space:pre-wrap;font-size:12pt;font-family:Times New Roman;font-kerning:none;min-width:fit-content;"> </font></p>
  <p style="font-size:10pt;margin-top:0;font-family:Times New Roman;margin-bottom:0;text-align:left;"><font style="white-space:pre-wrap;font-size:12pt;font-family:Times New Roman;font-kerning:none;min-width:fit-content;">&#160;</font></p>
  <p style="font-size:10pt;margin-top:0;font-family:Times New Roman;margin-bottom:0;text-align:left;"><font style="color:#000000;white-space:pre-wrap;font-size:12pt;font-family:Times New Roman;font-kerning:none;min-width:fit-content;">Under the terms of a power of attorney (the &#x201c;Power of Attorney&#x201d;) previously filed with the U.S. Securities and Exchange Commission, the undersigned was appointed an attorney-in-fact for Michael Paul Gray, as of October 10, 2024, to, among other things, execute for and on behalf of Michael Paul Gray any Forms 3, 4 or 5, Schedule 13D or 13G, or any amendment(s) thereto, in accordance with Section 16(a) of the Securities Exchange Act of 1934, as amended, and the rules thereunder.</font><font style="color:#000000;white-space:pre-wrap;font-size:12pt;font-family:Times New Roman;font-kerning:none;min-width:fit-content;"> </font></p>
  <p style="font-size:10pt;margin-top:0;font-family:Times New Roman;margin-bottom:0;text-align:left;"><font style="white-space:pre-wrap;font-size:12pt;font-family:Times New Roman;font-kerning:none;min-width:fit-content;">&#160;</font></p>
  <p style="font-size:10pt;margin-top:0;font-family:Times New Roman;margin-bottom:0;text-align:left;"><font style="color:#000000;white-space:pre-wrap;font-size:12pt;font-family:Times New Roman;font-kerning:none;min-width:fit-content;">In accordance with the authority granted under the Power of Attorney, including the full power of substitution, the undersigned hereby appoints Allison Ambrose as substitute attorney-in-fact, on behalf of Michael Paul Gray, with the power to exercise and execute all of the powers granted or conferred in the original Power of Attorney. For the avoidance of doubt, the foregoing appointment shall not serve as  a revocation of the powers granted to the undersigned himself in the Power of Attorney.</font><font style="color:#000000;white-space:pre-wrap;font-size:12pt;font-family:Times New Roman;font-kerning:none;min-width:fit-content;"> </font></p>
  <p style="font-size:10pt;margin-top:0;font-family:Times New Roman;margin-bottom:0;text-align:left;"><font style="white-space:pre-wrap;font-size:12pt;font-family:Times New Roman;font-kerning:none;min-width:fit-content;">&#160;</font></p>
  <p style="font-size:10pt;margin-top:0;font-family:Times New Roman;margin-bottom:0;text-align:left;"><font style="color:#000000;white-space:pre-wrap;font-size:12pt;font-family:Times New Roman;font-kerning:none;min-width:fit-content;">This substitute Power of Attorney shall remain in full force and effect until the underlying Power of Attorney is revoked or terminated, unless earlier revoked by the undersigned in a signed writing.</font></p>
  <p style="font-size:10pt;margin-top:0;font-family:Times New Roman;margin-bottom:0;text-align:left;"><font style="white-space:pre-wrap;font-size:12pt;font-family:Times New Roman;font-kerning:none;min-width:fit-content;">&#160;</font></p>
  <p style="font-size:10pt;margin-top:0;font-family:Times New Roman;margin-bottom:0;text-align:left;"><font style="color:#000000;white-space:pre-wrap;font-size:12pt;font-family:Times New Roman;font-kerning:none;min-width:fit-content;">Date: 12/19/24</font></p>
  <p style="font-size:10pt;margin-top:0;font-family:Times New Roman;margin-bottom:0;text-align:left;"><font style="color:#000000;white-space:pre-wrap;font-size:12pt;font-family:Times New Roman;font-kerning:none;min-width:fit-content;">By: </font><font style="color:#000000;white-space:pre-wrap;text-decoration:underline;font-size:12pt;font-family:Times New Roman;font-kerning:none;min-width:fit-content;">/s/ E. Rand Sutherland</font></p>
  <p style="font-size:10pt;margin-top:0;font-family:Times New Roman;margin-bottom:0;text-align:left;"><font style="color:#000000;white-space:pre-wrap;font-size:12pt;font-family:Times New Roman;font-kerning:none;min-width:fit-content;">Name: E. Rand Sutherland</font></p>
  <p style="font-size:10pt;margin-top:0;font-family:Times New Roman;margin-bottom:0;text-align:left;"><font style="color:#000000;white-space:pre-wrap;font-size:12pt;font-family:Times New Roman;font-kerning:none;min-width:fit-content;">Title: Attorney-in-Fact</font></p>
  <div class="page-node-content"><div style="z-index:-3;flex-direction:column;display:flex;padding-bottom:0.5in;min-height:1in;justify-content:flex-end;position:relative;box-sizing:border-box;"><p style="font-size:10pt;margin-top:0;font-family:Times New Roman;margin-bottom:0;text-align:left;"><font style="white-space:pre-wrap;font-size:12pt;font-family:Times New Roman;font-kerning:none;min-width:fit-content;">&#160;</font></p></div></div>
  <hr style="margin-inline-start:auto;margin-inline-end:auto;page-break-after:always;">
 </body>
</html>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
