ARCH Venture Partners XII, LLC - 13 Nov 2025 Form 4 Insider Report for Metsera, Inc. (MTSR)

Reporting relationship: Director, 10%+ Owner
Issuer ticker: MTSR
Reported as of: 13 Nov 2025
Net transaction value: $0
SEC form: 4
Accepted by SEC: 14 Nov 2025, 18:34:16 UTC
Prior SEC filing: 29 Oct 2025
Next SEC filing: 30 Apr 2026
Source filing: View source filing
Reporting owner signature: ARCH Venture Fund XII, L.P. By: ARCH Venture Partners XII, L.P., its General Partner By: ARCH Venture Partners XII, LLC, its General Partner By: /s/ Mark McDonnell, as Attorney-in-Fact

Key filing fact

ARCH Venture Partners XII, LLC filed Form 4 for Metsera, Inc. (MTSR) on 14 Nov 2025.

Key facts

This page summarizes ARCH Venture Partners XII, LLC's Form 4 filing for Metsera, Inc. (MTSR).
2 reported transactions and 0 derivative rows are listed below.
Accepted by SEC: 14 Nov 2025, 18:34.

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 (9)

CIK 0001979548 Primary reporting owner

ARCH Venture Partners XII, LLC

Relationship: Director, 10%+ Owner
Address: 8755 W. HIGGINS ROAD, SUITE 1025, CHICAGO
Signature: ARCH Venture Fund XII, L.P. By: ARCH Venture Partners XII, L.P., its General Partner By: ARCH Venture Partners XII, LLC, its General Partner By: /s/ Mark McDonnell, as Attorney-in-Fact
Signature date: 14 Nov 2025

CIK 0001906837

ARCH Venture Fund XII, L.P.

Relationship: Director, 10%+ Owner
Address: 8755 W. HIGGINS ROAD, SUITE 1025, CHICAGO
Signature: ARCH Venture Partners XII, L.P. By: ARCH Venture Partners XII, LLC, its General Partner By: /s/ Mark McDonnell, as Attorney-in-Fact
Signature date: 14 Nov 2025

CIK 0001979765

ARCH Venture Partners XII, L.P.

Relationship: Director, 10%+ Owner
Address: 8755 W. HIGGINS ROAD, SUITE 1025, CHICAGO
Signature: ARCH Venture Partners XII, LLC By: /s/ Mark McDonnell, as Attorney-in-Fact
Signature date: 14 Nov 2025

CIK 0002006772

ARCH Venture Fund XIII, L.P.

Relationship: Director, 10%+ Owner
Address: 8755 W. HIGGINS ROAD, SUITE 1025, CHICAGO
Signature: ARCH Venture Fund XIII, L.P. By: ARCH Venture Partners XIII, L.P., its General Partner By: ARCH Venture Partners XIII, LLC, its General Partner By: /s/ Mark McDonnell, as Attorney-in-Fact
Signature date: 14 Nov 2025

CIK 0002016083

ARCH Venture Partners XIII, L.P.

Relationship: Director, 10%+ Owner
Address: 8755 W. HIGGINS ROAD, SUITE 1025, CHICAGO
Signature: ARCH Venture Partners XIII, L.P. By: ARCH Venture Partners XIII, LLC, its General Partner By: /s/ Mark McDonnell, as Attorney-in-Fact
Signature date: 14 Nov 2025

CIK 0002016082

ARCH Venture Partners XIII, LLC

Relationship: Director, 10%+ Owner
Address: 8755 W. HIGGINS ROAD, SUITE 1025, CHICAGO
Signature: ARCH Venture Partners XIII, LLC By: /s/ Mark McDonnell, as Attorney-in-Fact
Signature date: 14 Nov 2025

CIK 0001219039

CRANDELL KEITH

Relationship: Director, 10%+ Owner
Address: C/O ARCH VENTURE PARTNERS IX, LLC, 8755 W. HIGGINS ROAD, SUITE 1025, CHICAGO
Signature: /s/ Keith Crandell, By: Mark McDonnell, attorney-in-fact
Signature date: 14 Nov 2025

CIK 0001229592

GILLIS STEVEN

Relationship: Director, 10%+ Owner
Address: C/O ARCH VENTURE PARTNERS, 8755 WEST HIGGINS ROAD, SUITE 1025, CHICAGO
Signature: /s/ Steven Gillis, By: Mark McDonnell, attorney-in-fact
Signature date: 14 Nov 2025

CIK 0001219042

NELSEN ROBERT

Relationship: Director, 10%+ Owner
Address: 8755 W. HIGGINS ROAD, SUITE 1025, CHICAGO
Signature: /s/ Robert Nelsen, By: Mark McDonnell, attorney-in-fact
Signature date: 14 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: -18,503,128
Change %: -100%
Price
Shares after: 0
Date: 13 Nov 2025
Ownership: See Footnote
Footnotes: F1, F2, F3

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, F4

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

Additional SEC filing notes

Filing notes and footnotes

Section 16 status

ARCH Venture Partners XII, LLC is no longer subject to Section 16 filing requirements. Form 4 or Form 5 obligations may still apply in specific circumstances.

Explanation of responses 4 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

Represents shares 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 F4

Represents shares 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 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.