Frazier Life Sciences Public Fund, L.P. - 18 Aug 2025 SCHEDULE 13D/A Report for MBX Biosciences, Inc. Common Stock, $0.0001 par value per share (MBX)

Filing manager
Frazier Life Sciences Public Fund, L.P.
Reporting owner
Patrick J. Heron
Security
MBX Biosciences, Inc. Common Stock, $0.0001 par value per share
Beneficially owned shares
4,557,097 shares
Ownership signal CIK-linked ownership evidence from parsed SEC filings. 2 signals
Large-stake signal

Form

SCHEDULE 13D/A

Active or control-oriented beneficial ownership filing.

Ownership

14%

Beneficial ownership of this reported class.

Shares

4,557,097 shares

Shares beneficially owned as disclosed.

Event date

18 Aug 2025

Date tied to the ownership event or amendment.

Accepted by SEC

20 Aug 2025

EDGAR acceptance date.

How to read this large-stake filing
  • Schedule 13D/G filings focus on beneficial ownership stakes, not a full portfolio.
  • Compare this filing with the holder history and issuer page before treating the percentage as a current position.
  • Use amendments to understand whether the disclosed stake increased, decreased, or changed reporting status.
Class ownership
14%
Subject security Names, identifiers, and filing context for this profile. 2 source fields
Symbol
MBX
Shares outstanding
33,508,066 shares
Source evidence Original filing metadata and source links for verification. 5 source fields
SEC form
SCHEDULE 13D/A
Accepted by SEC
20 Aug 2025, 17:23:18 UTC
Event date
18 Aug 2025
Next SEC filing
30 Sep 2025
Source filing
View source filing

Key filing fact

Frazier Life Sciences Public Fund, L.P. disclosed 14% ownership in MBX Biosciences, Inc. Common Stock, $0.0001 par value per share (MBX) on 18 Aug 2025.

Key facts

  • Frazier Life Sciences Public Fund, L.P. filed SCHEDULE 13D/A for MBX Biosciences, Inc. Common Stock, $0.0001 par value per share (MBX).
  • Disclosed ownership: 14%.
  • Date of event: 18 Aug 2025.

Change

  • No earlier schedule filing is available for direct comparison.
  • Current filing was accepted on 20 Aug 2025, 17:23.

Research use

  • This page turns one Schedule 13D/G filing into a quick large-stake read before the raw reporting-person rows.
  • Use the linked SEC filing as the source of truth for ownership percentages, shares, and reporting-party details.

Evidence

Backed by Schedule 13D/13G

Beneficial ownership values are sourced from the original SEC Schedule 13D/13G filing.

View source filing

Reporting persons

Disclosed reporting parties (17)

Names, ownership percentages, voting power, signatures, titles, and CIKs as disclosed in this Schedule 13D/G filing.

Name Ownership Shares owned Sole voting power Shared voting power Signature Title CIK
Frazier Life Sciences Public Fund, L.P. 3.3% 1,103,920 0 1,103,920 /s/ Steve R. Bailey By Steve R. Bailey, CFO of FHMLSP, L.L.C., GP of FHMLSP, L.P., GP of Frazier Life Sciences Public Fund, L.P. 0001863769
FHMLSP, L.P. 3.3% 1,103,920 0 1,103,920 /s/ Steve R. Bailey By Steve R. Bailey, CFO of FHMLSP, L.L.C., GP of FHMLSP, L.P. 0001879466
FHMLSP, L.L.C. 3.3% 1,103,920 0 1,103,920 /s/ Steve R. Bailey By Steve R. Bailey, CFO of FHMLSP, L.L.C. 0001879465
Frazier Life Sciences Public Overage Fund, L.P. 1% 325,653 0 325,653 /s/ Steve R. Bailey By Steve R. Bailey, CFO of FHMLSP Overage, L.L.C., GP of FHMLSP Overage, L.P., GP of Frazier Life Sciences Public Overage Fund, L.P. 0001913804
FHMLSP Overage, L.P. 1% 325,653 0 325,653 /s/ Steve R. Bailey By Steve R. Bailey, CFO of FHMLSP Overage, L.L.C., GP of FHMLSP Overage, L.P. 0001963247
FHMLSP Overage, L.L.C. 1% 325,653 0 325,653 /s/ Steve R. Bailey By Steve R. Bailey, CFO of FHMLSP Overage, L.L.C. 0001963248
Frazier Life Sciences X, L.P. 14% 4,552,774 0 4,552,774 /s/ Steve R. Bailey By Steve R. Bailey, CFO of FHMLS X, L.L.C., GP of FHMLS X, L.P., GP of Frazier Life Sciences X, L.P. 0001790879
FHMLS X, L.P. 14% 4,552,774 0 4,552,774 /s/ Steve R. Bailey By Steve R. Bailey, CFO of FHMLS X, L.L.C., GP of FHMLS X, L.P. 0001790880
FHMLS X, L.L.C. 14% 4,552,774 0 4,552,774 /s/ Steve R. Bailey By Steve R. Bailey, CFO of FHMLS X, L.L.C. 0001790811
Frazier Life Sciences XI, L.P. 0% 3,000 0 3,000 /s/ Steve R. Bailey By Steve R. Bailey, CFO of FHMLS XI, L.L.C., GP of FHMLS XI, L.P., GP of Frazier Life Sciences XI, L.P. 0001911592
FHMLS XI, L.P. 0% 3,000 0 3,000 /s/ Steve R. Bailey By Steve R. Bailey, CFO of FHMLS XI, L.L.C., GP of FHMLS XI, L.P. 0001911580
FHMLS XI, L.L.C. 0% 3,000 0 3,000 /s/ Steve R. Bailey By Steve R. Bailey, CFO of FHMLS XI, L.L.C. 0001911623
James N. Topper 14% 4,552,774 0 4,552,774 /s/ Steve R. Bailey By Steve R. Bailey, Attorney-in-Fact for James N. Topper, pursuant to a Power of Attorney, a copy of which was filed with the SEC on July 31, 2017 0001341382
Patrick J. Heron 14% 4,557,097 4,323 4,552,774 /s/ Steve R. Bailey By Steve R. Bailey, Attorney-in-Fact for Patrick J. Heron, pursuant to a Power of Attorney, a copy of which was filed with the SEC on July 31, 2017 0001365617
Albert Cha 0% 0 0 0 /s/ Steve R. Bailey By Steve R. Bailey, Attorney-in-Fact for Albert Cha, pursuant to a Power of Attorney, a copy of which was filed with the SEC on August 16, 2021 0001397906
James Brush 0% 0 0 0 /s/ Steve R. Bailey By Steve R. Bailey, Attorney-in-Fact for James Brush, pursuant to a Power of Attorney, a copy of which was filed with the SEC on August 16, 2021 0001865123
Daniel Estes 0% 0 0 0 /s/ Steve R. Bailey By Steve R. Bailey, Attorney-in-Fact for Daniel Estes, pursuant to a Power of Attorney, a copy of which was filed with the SEC on April 18, 2022 0001702527
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