[Form 4] Metsera, Inc. Insider Trading Activity

Rhea-AI Filing Summary

Metsera (MTSR)Pfizer effective on 11/13/2025. At closing, each share of Metsera common stock converted into the right to receive $65.60 in cash per share, plus one contingent value right (CVR) payable in cash upon achievement of specified milestones.

Equity awards were also settled under the merger terms. Outstanding stock options were canceled for a cash payment equal to the excess of $65.60 over the exercise price, multiplied by the number of underlying shares, plus one CVR per underlying share; unvested awards follow their schedule but fully vest on the first anniversary of closing, subject to continued service. RSUs were canceled for cash equal to $65.60 per underlying share plus the same number of CVRs, with no vesting conditions on those payments. The filing reflects director Kristina M. Burow’s positions, including indirect interests disclosed through ARCH Venture funds.

Insights

M&A and equity-compensation analyst

Neutral: Form 4 records merger consideration mechanics and award treatment.

The filing documents settlement mechanics after Metsera’s merger with Pfizer. Common stock converted into $65.60 cash per share plus one CVR, while options were canceled for cash based on intrinsic value and granted a CVR per underlying share. RSUs were converted into cash at $65.60 per unit plus one CVR each.

Unvested options retain timing constraints but fully vest on the first anniversary of closing, conditional on continued service; RSU payments have no vesting. These are standard post-acquisition treatments that align equity holders with deal consideration.

Because this is an administrative insider report reflecting a completed transaction, it is typically neutral for valuation. Actual CVR value depends on milestone achievement per the agreement.

11/13/2025 - 09:10 PM

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

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^*

Burow Kristina

(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
Common Stock	11/13/2025		D(1)(2)		17,070,904	D	(1)(2)	0	I	See footnote(8)
Common Stock	11/13/2025		D(1)(2)		18,503,128	D	(1)(2)	0	I	See footnote(8)
Common Stock	11/13/2025		D(1)(2)		7,523,682	D	(1)(2)	0	I	See footnote(9)
Common Stock	11/13/2025		D(1)(2)		8,313,680	D	(1)(2)	0	I	See footnote(9)

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)	$29.25	11/13/2025		D			16,125	(6)	05/19/2035	Common Stock	16,125	(3)(4)	0	D
Stock Option (right to buy)(3)(4)	$8.18	11/13/2025		D			148,953	(7)	11/11/2034	Common Stock	148,953	(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. There is no vesting applicable to the cash payment and the CVRs.

6. This option provided for vesting in 12 substantially equal monthly installments from May 20, 2025.

7. This option provided for vesting in 36 substantially equal monthly installments from November 12, 2024.

8. Represents shares of Common Stock held directly by ARCH Venture Fund XII, L.P ("ARCH Venture Fund XII"). ARCH Venture Partners XII, L.P. ("AVP XII LP"), as the sole general partner of ARCH Venture Fund XII, may be deemed to beneficially own the shares held by ARCH Venture Fund XII. ARCH Venture Partners XII, LLC ("AVP XII LLC"), as the sole general partner of AVP XII LP, may be deemed to beneficially own the shares held by ARCH Venture Fund XII. AVP XII LP and AVP XII LLC disclaim beneficial ownership except to the extent of any pecuniary interest therein. As members of the investment committee of AVP XII LLC, each of Kristina M. Burow, Keith Crandell, Steven Gillis and Robert Nelsen (the "AVP XII Committee Members") may also be deemed to share the power to direct the disposition and vote of the ARCH Venture Fund XII shares. Each AVP XII Committee Member disclaims beneficial ownership except to the extent of any pecuniary interest therein.

9. Represents shares of Common Stock held directly by ARCH Venture Fund XIII, L.P.("ARCH Venture Fund XIII"). ARCH Venture Partners XIII, L.P. ("AVP XIII LP"), as the sole general partner of ARCH Venture Fund XIII, may be deemed to beneficially own the shares held by ARCH Venture Fund XIII. ARCH Venture Partners XIII, LLC ("AVP XIII LLC"), as the sole general partner of AVP XIII LP, may be deemed to beneficially own the shares held by ARCH Venture Fund XIII. AVP XIII LP and AVP XIII LLC disclaim beneficial ownership except to the extent of any pecuniary interest therein. As members of the investment committee of AVP XIII LLC, each of Paul L. Berns, Kristina M. Burow, Keith Crandell, Steven Gillis and Robert Nelsen (the "AVP XIII Committee Members") may also be deemed to share the power to direct the disposition and vote of the ARCH Venture Fund XIII shares. Each AVP XIII Committee Member disclaims beneficial ownership except to the extent of any pecuniary interest therein.

	/s/ Matthew Lang, Attorney-in-Fact for Kristina M. Burow.	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).
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.

FAQ

What did Metsera (MTSR) shareholders receive at closing?

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

How were Metsera stock options treated in the Pfizer merger?

Each option was canceled for cash equal to ($65.60 − exercise price) × shares plus one CVR per underlying share; unvested amounts vest on the first anniversary, subject to service.

How were Metsera RSUs handled?

RSUs were canceled for $65.60 per underlying share in cash plus one CVR per unit, with no vesting conditions on those payments.

What is the transaction date shown in the Form 4?

The reported transactions occurred on 11/13/2025.

Who is the reporting person and their relationship to Metsera?

The reporting person is Kristina M. Burow, listed as a Director, including indirect interests via ARCH Venture funds.

What is a CVR in this context?

A CVR is a right to receive contingent cash payments if specified milestones are achieved, as defined in the CVR agreement.