[Form 4] Metsera, Inc. Insider Trading Activity

Rhea-AI Filing Summary

Metsera, Inc. (MTSR) filed a Form 4 reflecting transactions tied to its merger with Pfizer Inc.. At the merger’s Effective Time, each share of Metsera common stock was converted into the right to receive $65.60 in cash per share, plus one contingent value right (CVR) payable in cash upon specified milestones.

The reporting person’s holdings changed accordingly: 2,688 shares of common stock were disposed, leaving 0 shares beneficially owned. A restricted stock unit grant of 2,688 RSUs was reported; under the merger, RSUs were canceled and converted into cash equal to the cash amount per share times the RSU count and CVRs equal to the underlying shares, with these payments not subject to vesting. A stock option for 47,730 shares at $19.81 was canceled and exchanged for cash based on the excess of the cash amount over the exercise price, plus one CVR per underlying share. For unvested options, the cash and CVRs will vest on the first anniversary of closing, contingent on continued service.

Insights

Equity compensation and M&A specialist

Form 4 shows merger-driven cash and CVR treatment of equity.

The filing documents how Metsera equity converted at merger close: each share became $65.60 cash plus one CVR. Equity awards were canceled and exchanged for cash and CVRs per award mechanics. This is standard in cash acquisitions with contingent consideration.

For RSUs, payments equal to the cash amount per share times units and corresponding CVRs are not subject to vesting. For stock options, cash equals the excess of the cash amount over the exercise price times shares, plus CVRs per share; unvested awards’ consideration vests on the first anniversary of closing, subject to continued service. Actual holder proceeds depend on award counts and terms disclosed here.

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

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X

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^*

Stonehouse Jon P

(Last) (First) (Middle)

C/O METSERA, INC. 3 WORLD TRADE CENTER

175 GREENWICH STREET

(Street)

NEW YORK NY 10007

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
Metsera, Inc. [ MTSR ]

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

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

3. Date of Earliest Transaction (Month/Day/Year)
11/13/2025

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	11/13/2025		D(1)(2)		2,688	D	(1)(2)(5)	0	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
Restricted Stock Unit	$0	11/13/2025		A		2,688		(5)	(5)	Common Stock	2,688	(5)	2,688	D
Stock Option (right to buy)(3)(4)	$19.81	11/13/2025		D			47,730	(6)	04/27/2035	Common Stock	47,730	(3)(4)	0	D

Explanation of Responses:

1. Pursuant to the Agreement and Plan of Merger dated September 21, 2025, as amended on November 7, 2025 (the "Merger Agreement"), by and among Metsera, Inc. (the "Company"), Pfizer Inc., a Delaware corporation ("Parent"), and Mayfair Merger Sub, Inc., a Delaware corporation and a wholly owned subsidiary of the Parent (the "Merger Sub"), the Merger Sub merged with and into the Company, with the Company continuing as the surviving corporation and a wholly owned subsidiary of the Parent (the "Merger"). At the Effective Time of the Merger (as defined in the Merger Agreement), each issued and outstanding share of common stock, par value $0.00001 per share of the Company (the "Common Stock") was converted automatically into the right to receive (i) cash in an amount equal to $65.60 per share without interest (the "Closing Amount"), net of all applicable withholding taxes, plus

2. (Continued from footnote 1) (ii) one contractual contingent value right representing the right to receive contingent payments (a "CVR") in cash, without interest, upon the achievement of certain specified milestones, in accordance with the terms and conditions of the contingent value rights agreement entered into by the Parent and Equiniti Trust Company, LLC, dated November 13, 2025 (collectively, the "Merger Consideration").

3. Pursuant to the Merger Agreement, each outstanding and unexercised option immediately prior to the Effective Time, whether vested or unvested, was cancelled in exchange for the right to receive (x) an amount in cash equal to the product of (i) the excess, if any, of the Closing Amount minus the exercise price of such option, multiplied by (ii) the number of shares of Common Stock subject to such option immediately prior to the Effective Time, net of all applicable withholding taxes, and (y) one CVR for each share of the Common Stock subject to such stock option immediately prior to the Effective Time. In the case of any unvested stock options, the cash payment and the CVRs are subject to the same vesting schedule terms as were applicable to the stock options,

4. (Continued from footnote 3) except that all such payments will become vested upon the first anniversary of the closing of the Merger, subject to the holder's continued service with the Parent or its subsidiaries through the first anniversary of the Merger.

5. On November 12, 2025, the Reporting Person was granted restricted stock units ("RSUs") under the Company's 2025 Incentive Award Plan in a transaction exempt under Rule 16b-3. Each RSU represents a contingent right to receive one share of Common Stock. The RSUs vest in 36 substantially equal monthly installments from November 12, 2025. Pursuant to the Merger Agreement, all RSUs were cancelled and converted into the right to receive (x) an amount of cash equal to the Closing Amount multiplied by the number of shares of Common Stock subject to such RSU immediately prior to the Effective Time, net of all applicable withholding taxes, and (y) a number of CVRs equal to the under of the shares of Common Stock underlying the RSU. The cash payment and the CVRs are not subject to vesting.

6. This option provided for vesting in 36 substantially equal monthly installments from April 28, 2025.

	/s/ Matthew Lang Attorney-in-Fact for Jon P. Stonehouse	11/13/2025
	** 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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FAQ

What did Metsera (MTSR) shareholders receive in the merger?

Each share converted into $65.60 in cash plus one CVR payable upon specified milestones.

How were Metsera RSUs treated in the merger?

All RSUs were canceled and converted into cash equal to the cash amount per share times units and CVRs equal to the units, with payments not subject to vesting.

How were Metsera stock options treated?

Each option was canceled for cash equal to (cash amount − exercise price) × shares plus one CVR per share; unvested consideration vests on the first anniversary, subject to service.

What transactions did the reporting person record for common stock?

A disposal of 2,688 shares was reported, leaving 0 shares beneficially owned after the transaction.

What option position was reported and what was its exercise price?

A stock option for 47,730 shares with an $19.81 exercise price was canceled and exchanged as described.

Do unvested option-related payments vest immediately?

No. They vest on the first anniversary of closing, subject to continued service with the parent or its subsidiaries.