Kristina Burow - 13 Nov 2025 Form 4 Insider Report for Metsera, Inc. (MTSR)

Reporting relationship: Director
Issuer ticker: MTSR
Reported as of: 13 Nov 2025
Net transaction value: $0
SEC form: 4
Accepted by SEC: 13 Nov 2025, 21:10:04 UTC
Prior SEC filing: 29 Oct 2025
Next SEC filing: 24 Apr 2026
Source filing: View source filing
Reporting owner signature: /s/ Matthew Lang, Attorney-in-Fact for Kristina M. Burow.

Key filing fact

Kristina Burow filed Form 4 for Metsera, Inc. (MTSR) on 13 Nov 2025.

Key facts

This page summarizes Kristina Burow's Form 4 filing for Metsera, Inc. (MTSR).
8 reported transactions and 3 derivative rows are listed below.
Accepted by SEC: 13 Nov 2025, 21:10.

Change

Previous filing in this sequence was filed on 29 Oct 2025.
Current net transaction value: $0.

Research use

This tells you what this filing adds before you inspect full transaction and derivative tables.
You can trace every row back to the original SEC filing document.

Evidence

Filed on Form 4

Ownership activity is grounded in SEC Form 4 disclosures.

View source filing

Reporting Owners (1)

CIK 0001569248 Primary reporting owner

Burow Kristina

Relationship: Director
Address: C/O METSERA, INC. 3 WORLD TRADE CENTER, 175 GREENWICH STREET, NEW YORK
Signature: /s/ Matthew Lang, Attorney-in-Fact for Kristina M. Burow.
Signature date: 13 Nov 2025

Reported non-derivative transactions

Shares, units, or other non-derivative securities reported in this filing.

MTSR transaction

Common Stock

Disposed to Issuer

Transaction value
Shares: -2,688
Change %: -100%
Price
Shares after: 0
Date: 13 Nov 2025
Ownership: Direct
Footnotes: F1, F2, F5

MTSR transaction

Common Stock

Disposed to Issuer

Transaction value
Shares: -17,070,904
Change %: -100%
Price
Shares after: 0
Date: 13 Nov 2025
Ownership: See footnote
Footnotes: F1, F2, F8

MTSR transaction

Common Stock

Disposed to Issuer

Transaction value
Shares: -18,503,128
Change %: -100%
Price
Shares after: 0
Date: 13 Nov 2025
Ownership: See footnote
Footnotes: F1, F2, F8

MTSR transaction

Common Stock

Disposed to Issuer

Transaction value
Shares: -7,523,682
Change %: -100%
Price
Shares after: 0
Date: 13 Nov 2025
Ownership: See footnote
Footnotes: F1, F2, F9

MTSR transaction

Common Stock

Disposed to Issuer

Transaction value
Shares: -8,313,680
Change %: -100%
Price
Shares after: 0
Date: 13 Nov 2025
Ownership: See footnote
Footnotes: F1, F2, F9

Reported derivative securities

Options, warrants, convertible securities, or similar derivative positions disclosed in the filing.

MTSR transaction Derivative

Restricted Stock Unit

Award

Transaction value
Shares: +2,688
Change %
Price
Shares after: 2,688
Date: 13 Nov 2025
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 2,688
Exercise price: $0.000000
Footnotes: F5

MTSR transaction Derivative

Stock Option (right to buy)

Disposed to Issuer

Transaction value
Shares: -16,125
Change %: -100%
Price
Shares after: 0
Date: 13 Nov 2025
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 16,125
Exercise price: $29.25
Footnotes: F3, F4, F6

MTSR transaction Derivative

Stock Option (right to buy)

Disposed to Issuer

Transaction value
Shares: -148,953
Change %: -100%
Price
Shares after: 0
Date: 13 Nov 2025
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 148,953
Exercise price: $8.18
Footnotes: F3, F4, F7

^* marks a reported price that did not pass the local price check.

Additional SEC filing notes

Filing notes and footnotes

Section 16 status

Kristina Burow is no longer subject to Section 16 filing requirements. Form 4 or Form 5 obligations may still apply in specific circumstances.

Explanation of responses 9 footnotes

Footnote F1

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

Footnote F2

(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").

Footnote F3

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,

Footnote F4

(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.

Footnote F5

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.

Footnote F6

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

Footnote F7

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

Footnote F8

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.

Footnote F9

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.