<SEC-DOCUMENT>0000950170-25-085381-index.html : 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>
Document 1 - file: ownership.html

Document 1 - RAW XML: ownership.xml

</DOCUMENT>
<DOCUMENT>
<TYPE>EX-24.2
<SEQUENCE>2
<FILENAME>upb-ex24_2.htm
<DESCRIPTION>EX-24.2
<TEXT>
Document 2 - file: upb-ex24_2.htm

</DOCUMENT>
</SEC-DOCUMENT>