Upstream Bio (NASDAQ: UPB) grants RSUs, options to CMO Aaron Deykin

Rhea-AI Filing Summary

Upstream Bio, Inc. reported that its Chief Medical Officer, Aaron Deykin, received new equity awards on January 2, 2026. He was granted 32,000 restricted stock units (RSUs) of Common Stock at a grant price of $0, bringing his directly owned Common Stock to 33,581 shares as of that date, which includes 1,581 shares previously acquired under the 2024 Employee Stock Purchase Plan.

The filing also shows a grant of a stock option for 96,000 shares of Common Stock with an exercise price of $27.07 per share, expiring on January 1, 2036. The RSUs vest in sixteen equal quarterly installments after January 1, 2026, and the option vests in forty-eight equal monthly installments after the same date, in each case conditioned on Dr. Deykin’s continued service.

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^*

Deykin Aaron

(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)
	Chief Medical Officer

3. Date of Earliest Transaction (Month/Day/Year)
01/02/2026

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	01/02/2026		A(1)		32,000	A	$0	33,581(2)	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
Stock Option (Right to Buy)	$27.07	01/02/2026		A		96,000		(3)	01/01/2036	Common Stock	96,000	$0	96,000	D

Explanation of Responses:

1. 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.

2. Includes 1,581 shares of Common Stock previously acquired under the Issuer's 2024 Employee Stock Purchase Plan.

3. 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.

	/s/ Allison Ambrose, Attorney-in-Fact	01/06/2026
	** 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).
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FAQ

What insider transaction did Upstream Bio (UPB) report for Aaron Deykin?

The company reported that Chief Medical Officer Aaron Deykin received grants of 32,000 RSUs of Common Stock and a stock option for 96,000 shares on January 2, 2026.

How many Upstream Bio (UPB) shares does Aaron Deykin own after this Form 4?

After the reported RSU grant, Dr. Deykin beneficially owns 33,581 shares of Upstream Bio Common Stock directly, including 1,581 shares previously acquired under the 2024 Employee Stock Purchase Plan.

What are the vesting terms of the 32,000 RSUs granted to Upstream Bio CMO Aaron Deykin?

The 32,000 RSUs vest in sixteen equal quarterly installments following January 1, 2026, subject to Dr. Deykin’s continued service on each vesting date.

What are the key terms of Aaron Deykin’s 96,000-share stock option at Upstream Bio?

The stock option covers 96,000 shares of Common Stock at an exercise price of $27.07 per share, vests in forty-eight equal monthly installments after January 1, 2026, and expires on January 1, 2036, subject to his continued service.

Was Aaron Deykin’s Upstream Bio Form 4 transaction a purchase or sale in the open market?

No. The Form 4 reports equity grants: RSUs and a stock option awarded at a grant price of $0 for the RSUs, rather than open-market purchases or sales.

In what capacity is Aaron Deykin related to Upstream Bio (UPB) in this Form 4?

Dr. Deykin is listed as an officer of Upstream Bio, serving as its Chief Medical Officer, and the Form 4 is filed as a single reporting person.