<SEC-DOCUMENT>0000950170-25-085381.txt : 20250612
<SEC-HEADER>0000950170-25-085381.hdr.sgml : 20250612
<ACCEPTANCE-DATETIME>20250612161729
ACCESSION NUMBER:		0000950170-25-085381
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		2
CONFORMED PERIOD OF REPORT:	20250610
FILED AS OF DATE:		20250612
DATE AS OF CHANGE:		20250612

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Beckman Daniella
		CENTRAL INDEX KEY:			0001513422
		ORGANIZATION NAME:           	

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-42366
		FILM NUMBER:		251042680

	MAIL ADDRESS:	
		STREET 1:		C/O IDENIX PHARMACEUTICALS, INC.
		STREET 2:		ONE KENDALL SQUARE, BLDG. 1400
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Upstream Bio, Inc.
		CENTRAL INDEX KEY:			0002022626
		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]
		ORGANIZATION NAME:           	03 Life Sciences
		EIN:				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>2025-06-10</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001513422</rptOwnerCik>
            <rptOwnerName>Beckman Daniella</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>true</isDirector>
            <isOfficer>false</isOfficer>
            <isTenPercentOwner>false</isTenPercentOwner>
            <isOther>false</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>false</aff10b5One>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>11.59</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2025-06-10</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>false</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>17096</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2035-06-09</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>17096</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>17096</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The shares underlying this option shall vest upon the earlier of (i) June 10, 2026 and (ii) the date of the next Annual Meeting of Stockholders of the Issuer, subject to the Reporting Person's continued service on such vesting date.</footnote>
    </footnotes>

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

    <ownerSignature>
        <signatureName>/s/ Allison Ambrose, Attorney-in-Fact</signatureName>
        <signatureDate>2025-06-12</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
<DOCUMENT>
<TYPE>EX-24.2
<SEQUENCE>2
<FILENAME>upb-ex24_2.htm
<DESCRIPTION>EX-24.2
<TEXT>
<html>
 <head>
  <title>EX-24.2</title>
 </head>
 <body style="padding:8px;margin:auto!important;z-index:0;-webkit-text-size-adjust:100%;position:relative;">
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  <div class="main-content-container" style="z-index:5;position:relative;"><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="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="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 powers of attorney (each, a &#x201c;Power of Attorney&#x201d;) previously filed with the U.S. Securities and Exchange Commission, the undersigned was appointed an attorney-in-fact for the below listed individuals, as of October 10, 2024, to, among other things, execute for and on behalf of the following individuals 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></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;"> </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;">Daniella Beckman</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;">Erez Chimovits</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;">Aaron Deykin</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;">H. Edward Fleming, Jr.</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;">Adam Houghton</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;">Liam Ratcliffe</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;">Ronald C. Renaud, Jr.</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;">Marcella Kuhlman Ruddy</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;">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;"> </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 each Power of Attorney, including the full power of substitution, the undersigned hereby appoints Allison Ambrose as substitute attorney-in-fact, on behalf of the individuals listed above, 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 each Power of Attorney.</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;"> </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 with respect to each Power of Attorney until such 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="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="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 solid;font-size:12pt;font-family:Times New Roman;font-kerning:none;min-width:fit-content;">/s/ Michael Gray</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: Michael Gray</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><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;"> </font></p></div>
  <div style="z-index:2;flex-direction:column;display:flex;min-height:0.5in;justify-content:flex-end;position:relative;"></div>
  <hr style="margin-inline-start:auto;margin-inline-end:auto;page-break-after:always;">
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</html>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
