Upstream Bio CFO sells 853 shares to cover taxes

Upstream Bio, Inc. reported that CFO and COO Michael Gray sold 853 shares of common stock at $6.10 per share.

Rhea-AI Filing Summary

Upstream Bio, Inc. reported that CFO and COO Michael Gray sold 853 shares of common stock at $6.10 per share. After this transaction, he directly holds 28,795 shares. According to the disclosure, the sale was automatic under a sell-to-cover policy to satisfy tax withholding on vested restricted stock units.

Insider Trade Summary

Net Seller: 853 shares

Net Sell 1 txn

Insider GRAY MICHAEL

Role CFO and COO

Sold 853 shs ($5K)

Type	Security	Shares	Price	Value
Sale	Common Stock	853	$6.10	$5K

Holdings After Transaction: Common Stock — 28,795 shares (Direct)

Footnotes (1)

1. F1. 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.

Key Figures

Shares sold: 853 shares Sale price: $6.10 per share Shares held after sale: 28,795 shares +1 more

4 metrics

Shares sold 853 shares Common stock sold on 2026-06-16

Sale price $6.10 per share Average price for the 853-share sale

Shares held after sale 28,795 shares Direct ownership following the transaction

Net shares sold 853 shares Net sell direction in transaction summary

Key Terms

sell-to-cover, restricted stock units, tax withholding obligations, Form 4

4 terms

sell-to-cover financial

"The Issuer has adopted a "sell-to-cover" policy to satisfy the tax withholding obligations of the Reporting Person."

Sell-to-cover is when part of newly issued or exercised company stock is immediately sold to pay required taxes and fees, so the recipient keeps the remaining shares. For investors this matters because it reduces the number of shares insiders or employees actually hold after a grant, can create small, routine share sales that aren’t signal of cashing out, and slightly increases share supply on the market—like selling a portion of a paycheck to cover the tax bill.

restricted stock units financial

"to cover tax withholding obligations in connection with the vesting of restricted stock units."

Restricted stock units are a type of company reward where employees are promised shares of stock, but they only fully own these shares after meeting certain conditions, like staying with the company for a set time. They matter because they can become valuable assets and are often used to motivate employees to help the company succeed.

tax withholding obligations financial

"represent the number of shares required to be sold by the Reporting Person to cover tax withholding obligations in connection with the vesting"

Form 4 regulatory

"The sales reported on this Form 4 represent the number of shares required to be sold"

Form 4 is a official document that company insiders, such as executives or major shareholders, file with regulators whenever they buy or sell company shares. It provides transparency about how those with inside knowledge are trading, helping investors see if insiders are confident in the company's prospects or may be selling for personal reasons. This information can influence investor decisions by revealing insiders' perspectives on the company's value.

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

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

Upstream Bio reported that CFO and COO Michael Gray sold 853 shares of common stock. The shares were sold to cover tax withholding obligations tied to vested restricted stock units, under an automatic sell-to-cover policy adopted by the company.

At what price did the Upstream Bio (UPB) CFO’s shares sell?

The 853 shares of Upstream Bio common stock sold at an average price of $6.10 per share. This sale was executed automatically to satisfy tax withholding obligations related to restricted stock unit vesting, rather than as a discretionary open-market trade.

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

After selling 853 shares, Michael Gray directly owns 28,795 shares of Upstream Bio common stock. The filing indicates the sale was to cover tax withholding on vested restricted stock units, leaving the remaining shares as his ongoing equity position in the company.

Was the Upstream Bio (UPB) insider sale discretionary or automatic?

The sale was automatic. Upstream Bio has a sell-to-cover policy for tax withholding, and the reported 853-share sale represented the number of shares required to cover tax obligations from restricted stock unit vesting, not a discretionary timing decision by Michael Gray.

What is a sell-to-cover policy as used by Upstream Bio (UPB)?

A sell-to-cover policy automatically sells enough shares to pay tax withholding when stock awards vest. Upstream Bio’s policy caused the 853-share sale reported for Michael Gray, ensuring tax obligations on restricted stock units were met without requiring separate cash payments.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Accepted by SEC EDGAR 06/17/2026 - 04:05 PM EDT Learn about SEC filing dates

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
Estimated average burden
hours per response:			0.5

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 MASSACHUSETTS 02451

(City) (State) (Zip)

UNITED STATES

(Country)

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

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
06/16/2026

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

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

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

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	06/16/2026		S(1)		853	D	$6.1	28,795	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	06/17/2026
	** 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).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
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.
* Form 4: SEC 1474 (03-26)