<SEC-DOCUMENT>0000950170-25-021267-index.html : 20250214
<SEC-HEADER>0000950170-25-021267.hdr.sgml : 20250214
<ACCEPTANCE-DATETIME>20250214162329
ACCESSION NUMBER:		0000950170-25-021267
CONFORMED SUBMISSION TYPE:	SCHEDULE 13G
PUBLIC DOCUMENT COUNT:		2
FILED AS OF DATE:		20250214
DATE AS OF CHANGE:		20250214

SUBJECT COMPANY:	

	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

	FILING VALUES:
		FORM TYPE:		SCHEDULE 13G
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	005-94651
		FILM NUMBER:		25629363

	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

FILED BY:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			TCG Crossover GP I, LLC
		CENTRAL INDEX KEY:			0001839947
		ORGANIZATION NAME:           	
		IRS NUMBER:				000000000
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		SCHEDULE 13G

	BUSINESS ADDRESS:	
		STREET 1:		228 HAMILTON AVENUE, 3RD FLOOR
		CITY:			PALO ALTO
		STATE:			CA
		ZIP:			94301
		BUSINESS PHONE:		650-798-5495

	MAIL ADDRESS:	
		STREET 1:		228 HAMILTON AVENUE, 3RD FLOOR
		CITY:			PALO ALTO
		STATE:			CA
		ZIP:			94301
</SEC-HEADER>
<DOCUMENT>
<TYPE>SCHEDULE 13G
<SEQUENCE>1
<FILENAME>primary_doc.xml
<TEXT>
Document 1 - file: primary_doc.html

Document 1 - RAW XML: primary_doc.xml

</DOCUMENT>
<DOCUMENT>
<TYPE>EX-99.I
<SEQUENCE>2
<FILENAME>ck0001669811-ex99_i.pdf
<DESCRIPTION>EX-99.I
<TEXT>
Document 2 - file: ck0001669811-ex99_i.pdf

</DOCUMENT>
</SEC-DOCUMENT>