MICHAEL GRAY - 02 Jan 2026 Form 4 Insider Report for Upstream Bio, Inc. (UPB)

Role: CFO and COO
Signature: /s/ Allison Ambrose, Attorney-in-Fact
Issuer symbol: UPB
Transactions as of: 02 Jan 2026
Net transactions value: $0
Form type: 4
Filing time: 06 Jan 2026, 17:15:10 UTC
Previous filing: 07 Feb 2025
SEC: View on sec.gov

Reporting Owners (1)

Name	Relationship	Address	Signature	Signature date	CIK
GRAY MICHAEL	CFO and COO	UPSTREAM BIO, INC., 890 WINTER STREET, SUITE 200, WALTHAM	/s/ Allison Ambrose, Attorney-in-Fact	06 Jan 2026	0001271411

Transactions Table

Type	Sym	Class	Transaction	Value $	Shares	Change %	* Price $	Shares After	Date	Ownership	Footnotes
transaction	UPB	Common Stock	Award	$0	+30,500		$0.000000	30,500	02 Jan 2026	Direct	F1

Derivative Securities (e.g., puts, calls, warrants, options, convertible securities)

Type	Sym	Class	Transaction	Value $	Shares	Change %	* Price $	Shares After	Date	Underlying Class	Amount	Exercise Price	Ownership	Footnotes
transaction	UPB	Stock Option (Right to Buy)	Award	$0	+91,500		$0.000000	91,500	02 Jan 2026	Common Stock	91,500	$27.07	Direct	F2

* An asterisk sign (*) next to the price indicates that the price is likely invalid.

Explanation of Responses:

Id	Content
F1	Represents restricted stock units ("RSUs") granted pursuant to the Issuer's 2024 Stock Option and Incentive Plan. Each RSU represents the contingent right to receive one share of the Issuer's Common Stock upon vesting. The RSUs shall vest in sixteen equal quarterly installments following January 1, 2026, subject to the Reporting Person's continued service on each such vesting date.
F2	The shares underlying this option shall vest in forty-eight equal monthly installments following January 1, 2026, subject to the Reporting Person's continued service on each such vesting date.