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

Reporting relationship: CHIEF MEDICAL OFFICER
Issuer ticker: MTSR
Reported as of: 13 Nov 2025
Net transaction value: $0
SEC form: 4
Accepted by SEC: 13 Nov 2025, 21:20:07 UTC
Prior SEC filing: 22 May 2025
Source filing: View source filing
Reporting owner signature: /s/ Matthew Lang, Attorney-in-Fact for Steven Marso

Key filing fact

Steven Marso filed Form 4 for Metsera, Inc. (MTSR) on 13 Nov 2025.

Key facts

This page summarizes Steven Marso's Form 4 filing for Metsera, Inc. (MTSR).
5 reported transactions and 4 derivative rows are listed below.
Accepted by SEC: 13 Nov 2025, 21:20.

Change

Previous filing in this sequence was filed on 22 May 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 0002043242 Primary reporting owner

Marso Steven

Relationship: CHIEF MEDICAL OFFICER
Address: C/O METSERA, INC. 3 WORLD TRADE, CENTER 175 GREENWICH STREET, NEW YORK
Signature: /s/ Matthew Lang, Attorney-in-Fact for Steven Marso
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: -17,000
Change %: -100%
Price
Shares after: 0
Date: 13 Nov 2025
Ownership: Direct
Footnotes: F1, F2, F5

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: +17,000
Change %
Price
Shares after: 17,000
Date: 13 Nov 2025
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 17,000
Exercise price: $0.000000
Footnotes: F5

MTSR transaction Derivative

Stock Option (right to buy)

Disposed to Issuer

Transaction value
Shares: -120,000
Change %: -100%
Price
Shares after: 0
Date: 13 Nov 2025
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 120,000
Exercise price: $29.25
Footnotes: F3, F4, F6

MTSR transaction Derivative

Stock Option (right to buy)

Disposed to Issuer

Transaction value
Shares: -829,885
Change %: -100%
Price
Shares after: 0
Date: 13 Nov 2025
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 829,885
Exercise price: $0.2600
Footnotes: F3, F4, F7

MTSR transaction Derivative

Stock Option (right to buy)

Disposed to Issuer

Transaction value
Shares: -21,279
Change %: -100%
Price
Shares after: 0
Date: 13 Nov 2025
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 21,279
Exercise price: $0.2600
Footnotes: F3, F4, F8

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

Additional SEC filing notes

Filing notes and footnotes

Section 16 status

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

Explanation of responses 8 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. The cash payment and the CVRs are subject to the same vesting schedule terms as were applicable to the RSUs.

Footnote F6

This option provided for vesting in 48 substantially equal monthly installments from May 20, 2025.

Footnote F7

This option was fully vested as to 75% of the shares underlying the option and 25% was to be vested on May 26, 2026.

Footnote F8

This option was fully vested.