Upstream Bio CFO sells 853 shares at $5.49

Upstream Bio’s CFO and COO reported an automatic sell-to-cover stock sale tied to RSU vesting and related tax withholding.

Rhea-AI Filing Summary

Upstream Bio, Inc. (UPB) reported that its CFO and COO, Michael Gray, sold 853 shares of common stock on September 16, 2026 at $5.49 per share. According to the company’s sell-to-cover policy, this automatic sale was made solely to satisfy tax withholding obligations arising from the vesting of restricted stock units, not at the officer’s discretion. Following the transaction, Gray directly held 27,942 shares of Upstream Bio common stock.

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 F1	853	$5.49	$5K

Holdings After Transaction: Common Stock — 27,942 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 per share: $5.49 per share Shares held after transaction: 27,942 shares +1 more

4 metrics

Shares sold 853 shares Common stock sold by Michael Gray on September 16, 2026

Sale price per share $5.49 per share Price for the 853 Upstream Bio common shares sold

Shares held after transaction 27,942 shares Direct holdings of Michael Gray after the September 16, 2026 sale

Net shares sold 853 shares Net change in common stock holdings reported in this Form 4

Key Terms

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

3 terms

sell-to-cover financial

"The Issuer has adopted a "sell-to-cover" policy to satisfy the tax"

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

"in connection with the vesting of restricted stock units. Such sales"

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

"shares required to be sold by the Reporting Person to cover tax withholding obligations"

FAQ

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

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

Upstream Bio disclosed that CFO and COO Michael Gray sold 853 shares of common stock on September 16, 2026 at $5.49 per share. The sale was made to cover tax withholding obligations from vesting restricted stock units under a company sell-to-cover policy.

Was the UPB insider sale by Michael Gray discretionary?

No. The filing states the sale was automatic under a sell-to-cover policy to satisfy tax withholding obligations related to vesting restricted stock units and was not at Michael Gray’s discretion.

How many UPB shares does Michael Gray hold after this transaction?

After the September 16, 2026 sell-to-cover transaction, Michael Gray directly holds 27,942 shares of Upstream Bio common stock, according to the Form 4 filing.

What price did Michael Gray receive per UPB share in the reported sale?

Michael Gray’s reported sale of Upstream Bio common stock was executed at $5.49 per share for the 853 shares sold on September 16, 2026.

Why did Upstream Bio implement a sell-to-cover policy mentioned in this Form 4?

Upstream Bio adopted a sell-to-cover policy so that shares are automatically sold to cover tax withholding obligations when restricted stock units vest. The reported sale of 853 shares by Michael Gray reflects this policy in connection with an RSU vesting event.

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

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Available on EDGAR 09/17/2026 - 04:06 PM Accepted by SEC EDGAR 09/17/2026 - 04:05 PM 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)
09/16/2026

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	09/16/2026		S(1)		853	D	$5.49	27,942	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	09/17/2026
	** 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)