Upstream Bio (UPB) CFO executes automatic share sale to cover RSU taxes

Rhea-AI Filing Summary

Upstream Bio, Inc. CFO and COO Michael Gray reported an automatic sale of common stock primarily to cover taxes on vested restricted stock units. The transaction involved 852 shares of common stock sold at $9.29 per share. After this sell-to-cover transaction, he directly holds 29,648 common shares. The company has a sell-to-cover policy, and the sale was carried out automatically, not at his discretion.

Insights

Equity compensation analyst

Routine sell-to-cover sale with limited informational value.

The filing shows Upstream Bio CFO and COO Michael Gray sold 852 common shares at $9.29 per share. A footnote explains the sale was automatic under a company sell-to-cover policy tied to restricted stock unit vesting.

This means shares were sold solely to satisfy tax withholding obligations, a common mechanism for equity awards. Such transactions typically carry weak signaling value about management’s view of the stock, especially as Gray continues to directly hold 29,648 shares after the sale.

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
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Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

GRAY MICHAEL

(Last) (First) (Middle)

UPSTREAM BIO, INC.

890 WINTER STREET, SUITE 200

(Street)

WALTHAM MA 02451

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
Upstream Bio, Inc. [ UPB ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	CFO and COO

3. Date of Earliest Transaction (Month/Day/Year)
03/16/2026

4. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	03/16/2026		S(1)		852	D	$9.29	29,648	D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

Explanation of Responses:

1. The Issuer has adopted a "sell-to-cover" policy to satisfy the tax withholding obligations of the Reporting Person. The sales reported on this Form 4 represent the number of shares required to be sold by the Reporting Person to cover tax withholding obligations in connection with the vesting of restricted stock units. Such sales were automatic and not at the discretion of the Reporting Person.

	/s/ Allison Ambrose, Attorney-in-Fact	03/17/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
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Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.

FAQ

What insider transaction did Upstream Bio (UPB) report for Michael Gray?

Upstream Bio reported that CFO and COO Michael Gray sold 852 common shares at $9.29 per share. According to the filing, this sale was executed under a sell-to-cover policy to satisfy tax withholding obligations from restricted stock unit vesting.

Was Michael Gray’s Upstream Bio (UPB) share sale discretionary?

The sale was not discretionary. A footnote states Upstream Bio uses a sell-to-cover policy and the 852 shares were sold automatically to cover tax withholding obligations related to restricted stock units that vested for Michael Gray.

How many Upstream Bio (UPB) shares does Michael Gray hold after the sale?

Following the reported transaction, Michael Gray directly holds 29,648 shares of Upstream Bio common stock. This context shows the 852 shares sold for tax withholding represent a relatively small portion of his overall direct holdings.

What price was received for the Upstream Bio (UPB) shares sold by Michael Gray?

The 852 Upstream Bio common shares were sold at an average price of $9.29 per share. The filing characterizes this as an open-market sale executed under a company sell-to-cover policy for tax withholding obligations on vested restricted stock units.

Why did Upstream Bio (UPB) implement a sell-to-cover policy for insiders?

The filing explains that Upstream Bio adopted a sell-to-cover policy to satisfy insiders’ tax withholding obligations on equity awards. For Michael Gray, the reported 852-share sale covered taxes arising from the vesting of restricted stock units, simplifying tax payments without requiring separate cash outlays.