# EDGAR Filing Document

**Accession Number:** 0001055951
**File Stem:** 0000947871-26-000114
**Filing Date:** 2026-2
**Character Count:** 23798
**Document Hash:** bb346564cdb11ee2484d7ca1830ca24a
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0000947871-26-000114.hdr.sgml**: 20260211

**ACCESSION NUMBER**: 0000947871-26-000114

**CONFORMED SUBMISSION TYPE**: SCHEDULE 13D/A

**PUBLIC DOCUMENT COUNT**: 2

**FILED AS OF DATE**: 20260211

**DATE AS OF CHANGE**: 20260211

**SUBJECT COMPANY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** MBX Biosciences, Inc.
- **CENTRAL INDEX KEY:** 0001776111
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 000000000
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** SCHEDULE 13D/A
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 005-94623
- **FILM NUMBER:** 26622557

**BUSINESS ADDRESS:**
- **STREET 1:** 11711 N. MERIDIAN STREET
- **STREET 2:** SUITE 300
- **CITY:** CARMEL
- **STATE:** IN
- **ZIP:** 46032
- **BUSINESS PHONE:** 3179893100

**MAIL ADDRESS:**
- **STREET 1:** 11711 N. MERIDIAN STREET
- **STREET 2:** SUITE 300
- **CITY:** CARMEL
- **STATE:** IN
- **ZIP:** 46032
**FILED BY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** ORBIMED ADVISORS LLC
- **CENTRAL INDEX KEY:** 0001055951

**ORGANIZATION NAME:**
- **EIN:** 133976876
- **STATE OF INCORPORATION:** DE

**FILING VALUES:**
- **FORM TYPE:** SCHEDULE 13D/A

**BUSINESS ADDRESS:**
- **STREET 1:** 601 LEXINGTON AVENUE
- **STREET 2:** 54TH FLOOR
- **CITY:** NEW YORK
- **STATE:** NY
- **ZIP:** 10022
- **BUSINESS PHONE:** (212) 739-6400

**MAIL ADDRESS:**
- **STREET 1:** 601 LEXINGTON AVENUE
- **STREET 2:** 54TH FLOOR
- **CITY:** NEW YORK
- **STATE:** NY
- **ZIP:** 10022

## Exhibit 99.1

**<u>Exhibit 1</u>**

JOINT FILING AGREEMENT

The undersigned hereby agree that Amendment No. 2 to the Statement on Schedule 13D, dated February 5, 2026, with respect to the common stock, par value $0.0001 per share, of MBX Biosciences, Inc. is filed on behalf of each of us pursuant to and in accordance with the provisions of Rule 13d-1(k) under the Securities Exchange Act of 1934, as amended. Each of the undersigned agrees to be responsible for the timely filing of this Statement, and for the completeness and accuracy of the information concerning itself contained therein. This Joint Filing Agreement may be executed in any number of counterparts, all of which taken together shall constitute one and the same instrument.

IN WITNESS WHEREOF, the undersigned have executed this Joint Filing Agreement as of the 11<sup>th</sup> day of February 2026.

---

| | |
|:---|:---|
| ORBIMED ADVISORS LLC | ORBIMED ADVISORS LLC |
| By: | <u>/s/ Carl L. Gordon</u> |
|  | Name: Carl L. Gordon |
|  | Title: Member |
| ORBIMED CAPITAL GP VII LLC | ORBIMED CAPITAL GP VII LLC |
| By: | ORBIMED ADVISORS LLC, its managing member |
| By: | <u>/s/ Carl L. Gordon</u> |
|  | Name: Carl L. Gordon |
|  | Title: Member of OrbiMed Advisors LLC |
| ORBIMED GENESIS GP LLC | ORBIMED GENESIS GP LLC |
| By: | ORBIMED ADVISORS LLC, its managing member |
| By: | <u>s/ Carl L. Gordon</u> |
|  | Name: Carl L. Gordon |
|  | Title: Member of OrbiMed Advisors LLC |

---

### UNITED STATES SECURITIES AND EXCHANGE COMMISSION
**Washington, D.C. 20549**

## SCHEDULE 13D

### Under the Securities Exchange Act of 1934

**(Amendment No. 2)**

**MBX Biosciences, Inc.**

*(Name of Issuer)*

**COMMON STOCK**

*(Title of Class of Securities)*

**55287L101**

*(CUSIP Number)*

**OrbiMed Advisors LLC**<br>601 Lexington Avenue, 54th Floor<br>New York NY 10022<br>(212) 739-6400

*(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)*

**02/05/2026**

*(Date of Event Which Requires Filing of this Statement)*

| **CUSIP No.** | **55287L101** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**ORBIMED ADVISORS LLC** | Name of reporting person<br>**ORBIMED ADVISORS LLC** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**DELAWARE** | Citizenship or place of organization<br>**DELAWARE** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**3637887.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**3637887.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**3637887.00** | Aggregate amount beneficially owned by each reporting person<br>**3637887.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**7.7%** | Percent of class represented by amount in Row (11)<br>**7.7%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**IA** | Type of Reporting Person (See Instructions)<br>**IA** | |

---

| **CUSIP No.** | **55287L101** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**ORBIMED CAPITAL GP VII LLC** | Name of reporting person<br>**ORBIMED CAPITAL GP VII LLC** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**DELAWARE** | Citizenship or place of organization<br>**DELAWARE** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**2958000.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**2958000.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**2958000.00** | Aggregate amount beneficially owned by each reporting person<br>**2958000.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**6.3%** | Percent of class represented by amount in Row (11)<br>**6.3%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**OO** | Type of Reporting Person (See Instructions)<br>**OO** | |

---

| **CUSIP No.** | **55287L101** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**OrbiMed Genesis GP LLC** | Name of reporting person<br>**OrbiMed Genesis GP LLC** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**DELAWARE** | Citizenship or place of organization<br>**DELAWARE** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**679887.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**679887.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**679887.00** | Aggregate amount beneficially owned by each reporting person<br>**679887.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**1.4%** | Percent of class represented by amount in Row (11)<br>**1.4%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**OO** | Type of Reporting Person (See Instructions)<br>**OO** | |

---

**Item 1. Security and Issuer**

**(a) Title of Class of Securities:**
COMMON STOCK

**(b) Name of Issuer:**
MBX Biosciences, Inc.

**(c) Address of Issuer's Principal Executive Offices:**
11711 N. Meridian Street, Suite 300, Carmel, IN, 46032

This Amendment No. 2 ("Amendment No. 2") to Schedule 13D supplements and amends the Statement on Schedule 13D of OrbiMed Advisors LLC ("OrbiMed Advisors"), OrbiMed Capital GP VII LLC, ("GP VII"), and OrbiMed Genesis GP LLC ("OrbiMed Genesis") (collectively, the "Reporting Persons") originally filed with the Securities and Exchange Commission (the "SEC") on September 23, 2024 and amended by Amendment No. 1 thereto filed with the SEC on September 30, 2025. This Amendment No. 2 is being filed to report that the beneficial ownership of the outstanding Shares held by the Reporting Persons decreased by more than 1% as a result of an increase in the number of Shares outstanding.

**Item 4. Purpose of Transaction**

The Reporting Persons from time to time intend to review their investment in the Issuer on the basis of various factors, including the Issuer's business, financial condition, results of operations and prospects, general economic and industry conditions, the securities markets in general and those for the Issuer's Shares in particular, as well as other developments and other investment opportunities. Based upon such review, the Reporting Persons will take such actions in the future as the Reporting Persons may deem appropriate in light of the circumstances existing from time to time. If the Reporting Persons believe that further investment in the Issuer is attractive, whether because of the market price of Shares or otherwise, they may acquire Shares or other securities of the Issuer either in the open market or in privately negotiated transactions. Similarly, depending on market and other factors, the Reporting Persons may determine to dispose of some or all of the Shares currently owned by the Reporting Persons or otherwise acquired by the Reporting Persons either in the open market or in privately negotiated transactions.

Except as set forth in this Schedule 13D, the Reporting Persons have not formulated any plans or proposals which relate to or would result in:  (a) the acquisition by any person of additional securities of the Issuer or the disposition of securities of the Issuer, (b) an extraordinary corporate transaction, such as a merger, reorganization or liquidation, involving the Issuer or any of its subsidiaries, (c) a sale or transfer of a material amount of the assets of the Issuer or any of its subsidiaries, (d) any change in the present Board of Directors or management of the Issuer, including any plans or proposals to change the number or term of directors or to fill any existing vacancies on the board, (e) any material change in the Issuer's capitalization or dividend policy of the Issuer, (f) any other material change in the Issuer's business or corporate structure, (g) any change in the Issuer's charter or bylaws or other instrument corresponding thereto or other action which may impede the acquisition of control of the Issuer by any person, (h) causing a class of the Issuer's securities to be deregistered or delisted from a national securities exchange or to cease to be authorized to be quoted in an inter-dealer quotation system of a registered national securities association, (i) a class of equity securities of the Issuer becoming eligible for termination of registration pursuant to Section 12(g)(4) of the Act or (j) any action similar to any of those enumerated above.

**Item 5. Interest in Securities of the Issuer**

**(a)**
The following disclosure is based upon 47,153,288 outstanding Shares, which amount includes 44,902,302 Shares as set forth in the Issuer's Quarterly Report on Form 10-Q filed with the SEC on November 6, 2025 plus 2,250,986 additional Shares issued in connection with an at-the-market offering program as set forth in the Issuer's Current Report on Form 8-K filed with the SEC on February 5, 2026.

As of the date of this filing, OrbiMed Private Investments VII, LP ("OPI VII"), a limited partnership organized under the laws of Delaware, holds 2,958,000 Shares, constituting approximately 6.3% of the issued and outstanding Shares. GP VII is the general partner of OPI VII, pursuant to the terms of the limited partnership agreement of OPI VII, and OrbiMed Advisors is the managing member of GP VII, pursuant to the terms of the limited liability company agreement of GP VII. As a result, OrbiMed Advisors and GP VII share power to direct the vote and disposition of the Shares held by OPI VII and may be deemed directly or indirectly, including by reason of their mutual affiliation, to be the beneficial owners of the Shares held by OPI VII. OrbiMed Advisors exercises this investment and voting power through a management committee comprised of Carl L. Gordon, Sven H. Borho, and W. Carter Neild, each of whom disclaims beneficial ownership of the Shares held by OPI VII.

In addition, OrbiMed Advisors and GP VII, pursuant to their authority under the limited partnership agreement of OPI VII, caused OPI VII to enter into the agreements referred to in Item 6 below.

As of the date of this filing, OrbiMed Genesis Master Fund, L.P. ("Genesis"), a limited partnership organized under the laws of the Cayman Islands, holds 679,887 Shares, constituting approximately 1.4% of the issued and outstanding Shares. OrbiMed Genesis is the general partner of Genesis, pursuant to the terms of the limited partnership agreement of Genesis, and OrbiMed Advisors is the managing member of OrbiMed Genesis, pursuant to the terms of the limited liability company agreement of OrbiMed Genesis. As a result, OrbiMed Advisors and OrbiMed Genesis share power to direct the vote and disposition of the Shares held by Genesis and may be deemed, directly or indirectly, including by reason of their mutual affiliation, to be the beneficial owners of the Shares held by Genesis. OrbiMed Advisors exercises this investment and voting power through a management committee comprised of Carl L. Gordon, Sven H. Borho and W. Carter Neild, each of whom disclaims beneficial ownership of the Shares held by Genesis.

In addition, OrbiMed Advisors and OrbiMed Genesis, pursuant to their authority under the limited partnership agreement of Genesis, caused Genesis to enter into the agreements referred to in Item 6 below.

**(b)**
Item 5(a) is incorporated by reference herein.

**(c)**
On December 26, 2025, GEN sold 2,223 Shares at a price of $31.03.
On December 26, 2025, OPI VII sold 9,708 Shares at a price of $31.03.
On December 29, 2025, GEN sold 5,483 Shares at a price of $31.23.
On December 29, 2025, OPI VII sold 23,950 Shares at a price of $31.23.
On December 31, 2025, GEN sold 4,903 Shares at a price of $31.58.
On December 31, 2025, OPI VII sold 21,417 Shares at a price of $31.58.
On January 7, 2026, GEN sold 7,567 Shares at a price of $32.88.
On January 7, 2026, OPI VII sold 33,049 Shares at a price of $32.88.
On January 8, 2026, GEN sold 329 Shares at a price of $31.28.
On January 8, 2026, OPI VII sold 1,436 Shares at a price of $31.28.
On January 9, 2026, GEN sold 6,381 Shares at a price of $31.46.
On January 9, 2026, OPI VII sold 27,870 Shares at a price of $31.46.
On January 12, 2026, GEN sold 18,630 Shares at a price of $35.01.
On January 12, 2026, OPI VII sold 81,370 Shares at a price of $35.01.
On January 13, 2026, GEN sold 3,863 Shares at a price of $36.09.
On January 13, 2026, OPI VII sold 16,874 Shares at a price of $36.09.
On January 14, 2026, GEN sold 10,237 Shares at a price of $40.08.
On January 14, 2026, OPI VII sold 44,710 Shares at a price of $40.08.
On January 15, 2026, GEN sold 1,304 Shares at a price of $42.09.
On January 15, 2026, OPI VII sold 5,696 Shares at a price of $42.09.
On January 16, 2026, GEN sold 7,080 Shares at a price of $40.91.
On January 16, 2026, OPI VII sold 30,920 Shares at a price of $40.91.

The Reporting Persons undertake, upon request by the staff of the SEC or the Issuer to provide full information regarding the number of Shares sold at each separate price.

**Item 6. Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer.**

In addition to the relationships between the Reporting Persons described in Items 2 and 5 above, GP VII is the general partner of OPI VII, pursuant to the terms of the limited partnership agreement of OPI VII. Pursuant to this agreement and relationship, GP VII has discretionary investment management authority with respect to the assets of OPI VII. Such authority includes the power to vote and otherwise dispose of securities held by OPI VII. The number of outstanding Shares of the Issuer attributable to OPI VII is 2,958,000 Shares. GP VII, pursuant to its authority under the limited partnership agreement of OPI VII, may be considered to hold indirectly 2,958,000 Shares.

OrbiMed Genesis is the general partner of Genesis, pursuant to the terms of the limited partnership agreement of Genesis. Pursuant to this agreement and relationship, OrbiMed Genesis has discretionary investment management authority with respect to the assets of Genesis. Such authority includes the power to vote and otherwise dispose of securities held by Genesis. The number of outstanding Shares of the Issuer attributable to Genesis is 679,887 Shares. OrbiMed Genesis, pursuant to its authority under the limited partnership agreement of Genesis, may be considered to hold indirectly 679,887 Shares.

In addition to the relationships between the Reporting Persons described in Items 2 and 5 above, OrbiMed Advisors is the managing member of GP VII and OrbiMed Genesis, pursuant to the terms of the limited liability company agreements of GP VII and OrbiMed Genesis. Pursuant to these agreements and relationships, OrbiMed Advisors and GP VII have discretionary investment management authority with respect to the assets of OPI VII, and OrbiMed Advisors and OrbiMed Genesis have discretionary investment management authority with respect to the assets of Genesis. Such authority includes the power of GP VII to vote and otherwise dispose of securities held by OPI VII and OrbiMed Genesis to vote and otherwise dispose of securities held by Genesis. The number of outstanding Shares attributable to OPI VII is 2,958,000 Shares, and the number of outstanding Shares attributable to Genesis is 679,887 Shares. OrbiMed Advisors, pursuant to its authority under the terms of the limited liability company agreements of GP VII and Genesis may also be considered to hold indirectly 3,637,887 Shares.

Investors' Rights Agreement

In addition, OPI VII, Genesis, and certain other stockholders of the Issuer entered into a Second Amended and Restated Investors' Rights Agreement with the Issuer, dated as of August 2, 2024 (the "Investors' Rights Agreement"). Pursuant to the Investors' Rights Agreement and subject to the terms and conditions therein, the parties agreed that:

Demand Registration Rights

At any time beginning 180 days following the effective date of the registration statement of the IPO, the holders of at least 40% of the Issuer's registrable securities may request that the Issuer file a registration statement under the Securities Act of 1933, as amended (the "Securities Act") on a Form S-1 at the Issuer's expense, subject to certain exceptions, with an anticipated aggregate offering price, net of offering expenses, of not less than $10 million, in which case the Issuer will be required to effect the registration as soon as practicable, and in any event within 60 days after the date of such registration request. The Issuer is not obligated to effect more than one of these registrations.

Form S-3 Registration Rights

At any time after the Issuer is qualified to file a registration statement on Form S-3 under the Securities Act, and subject to limitations and conditions specified in the Investors' Rights Agreement, holders of at least 20% of the registrable securities under the Investors' Rights Agreement may request that the Issuer prepare and file a registration statement on Form S-3 at the Issuer's expense covering the Shares of such holders having an anticipated aggregate offering price, net of offering expenses, of at least $5 million, in which case the Issuer will be required to effect the registration as soon as practicable, and in any event within 45 days after receiving such request. The Issuer is not obligated to effect more than two of these registrations in any 12-month period.

Piggyback Registration Rights

Whenever the Issuer proposes to file a registration statement under the Securities Act, other than with respect to certain excluded registrations, OPI VII and Genesis will each be entitled to notice of the registration and have the right, subject to limitations that the underwriters may impose on the number of Shares included in the registration, to include the Shares held by them in the registration.

The foregoing description of the Investors' Rights Agreement does not purport to be complete and is qualified in its entirety by reference to the full text of the Investors' Rights Agreement, which is filed as Exhibits 2 and incorporated herein by reference.

### SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

**Reporting Person:** ORBIMED ADVISORS LLC

**Signature:** /s/ Carl L. Gordon

**Name/Title:** Carl L. Gordon/Member

**Date:** 02/11/2026

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

**Reporting Person:** ORBIMED CAPITAL GP VII LLC

**Signature:** /s/ Carl L. Gordon

**Name/Title:** Carl L. Gordon/Member of OrbiMed Advisors LLC

**Date:** 02/11/2026

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

**Reporting Person:** OrbiMed Genesis GP LLC

**Signature:** /s/ Carl L. Gordon

**Name/Title:** Carl L. Gordon/Member of OrbiMed Advisors LLC

**Date:** 02/11/2026