Upstream Bio (UPB) CBO auto-sells shares to cover RSU tax

Rhea-AI Filing Summary

Upstream Bio, Inc. Chief Business Officer Adam Houghton reported an automatic sale of common stock tied to tax withholding on vested restricted stock units. He sold 700 shares at $6.10 per share under the company’s sell-to-cover policy, which executes sales without his discretion. After this transaction, he directly holds 23,601 shares of Upstream Bio common stock, so the filing reflects tax-related administration rather than a discretionary change in his investment position.

Insider Trade Summary

Net Seller: 700 shares ($4,270)

Net Sell 1 txn

Insider Houghton Adam

Role Chief Business Officer

Sold 700 shs ($4K)

Type	Security	Shares	Price	Value
Sale	Common Stock	700	$6.10	$4K

Holdings After Transaction: Common Stock — 23,601 shares (Direct, null)

Footnotes (1)

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Key Figures

Shares sold: 700 shares Sale price: $6.10 per share Shares held after: 23,601 shares

3 metrics

Shares sold 700 shares Common stock sold on 2026-06-16 to cover tax withholding

Sale price $6.10 per share Open-market sale associated with RSU vesting

Shares held after 23,601 shares Direct Upstream Bio common stock holdings after transaction

Key Terms

sell-to-cover, restricted stock units, Form 4

3 terms

sell-to-cover financial

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

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

"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.

Form 4 regulatory

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

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.

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Form 4 Insider Transactions: What Each Field Means →

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^*

Houghton Adam

(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)
	Chief Business Officer

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)		700	D	$6.1	23,601	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)

FAQ

What insider transaction did Upstream Bio (UPB) report for Adam Houghton?

Upstream Bio reported that Chief Business Officer Adam Houghton sold 700 common shares at $6.10 each. The sale was triggered automatically to cover tax withholding on newly vested restricted stock units under the company’s sell-to-cover policy.

Was Adam Houghton’s Upstream Bio (UPB) share sale discretionary?

The sale was not discretionary. A company sell-to-cover policy required selling 700 shares to satisfy tax withholding from restricted stock unit vesting, and the transaction occurred automatically rather than by Houghton’s active trading decision.

How many Upstream Bio (UPB) shares does Adam Houghton hold after this sale?

After selling 700 shares to cover tax withholding, Adam Houghton directly holds 23,601 shares of Upstream Bio common stock. This indicates that the transaction affected only a portion of his overall equity position in the company.

What price was received per share in Adam Houghton’s Upstream Bio (UPB) sale?

The reported transaction shows 700 Upstream Bio common shares sold at $6.10 per share. This price reflects the execution level for the automatic sell-to-cover sale associated with the vesting of restricted stock units.

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

Upstream Bio’s policy uses automatic share sales to cover executives’ tax withholding obligations upon restricted stock unit vesting. This approach satisfies required tax payments in shares, limiting the need for executives to separately fund cash tax liabilities.