# EDGAR Filing Document

**Accession Number:** 0001776111
**File Stem:** 0001193125-26-103122
**Filing Date:** 2026-3
**Character Count:** 22274
**Document Hash:** 9e85f543860007c4b343f427ecd13f34
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001193125-26-103122.hdr.sgml**: 20260312

**ACCESSION NUMBER**: 0001193125-26-103122

**CONFORMED SUBMISSION TYPE**: S-8

**PUBLIC DOCUMENT COUNT**: 15

**FILED AS OF DATE**: 20260312

**DATE AS OF CHANGE**: 20260312

**EFFECTIVENESS DATE**: 20260312

**FILER**: 

**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:** S-8
- **SEC ACT:** 1933 Act
- **SEC FILE NUMBER:** 333-294228
- **FILM NUMBER:** 26745726

**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

**As filed with the Securities and Exchange Commission on March 12, 2026** 

**Registration No. 333-** 

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**UNITED STATES** 

**SECURITIES AND EXCHANGE COMMISSION** 

**Washington, D.C. 20549** 

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**FORM S-8** 

**REGISTRATION STATEMENT** 

***Under*** 

***The Securities Act of 1933*** 

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**MBX Biosciences, Inc.** 

**(Exact name of registrant as specified in its charter)** 

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| | |
|:---|:---|
| **Delaware** | **84-1882872** |
| **(State or other jurisdiction of**<br>**incorporation or organization)** | **(I.R.S. Employer**<br>**Identification No.)** |

---

**MBX Biosciences, Inc.** 

**11711 N. Meridian Street, Suite 300** 

**Carmel, Indiana 46032** 

**(317) 659-0200** 

**(Address, including zip code and telephone number, including area code, of Registrant's principal executive offices)** 

**MBX Biosciences, Inc. 2024 Stock Option and Incentive Plan** 

**MBX Biosciences, Inc. 2024 Employee Stock Purchase Plan** 

**(Full title of the plans)** 

**P. Kent Hawryluk** 

**President and Chief Executive Officer** 

**MBX Biosciences, Inc.** 

**11711 N. Meridian Street, Suite 300** 

**Carmel, Indiana 46032** 

**(317) 659-0200** 

**(Name, address, including zip code, and telephone number, including area code, of agent for service)** 

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***Copies to:*** 

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**Mitchell S. Bloom** 

**Edwin M. O'Connor** 

**Goodwin Procter LLP** 

**100 Northern Avenue** 

**Boston, Massachusetts 02210** 

**(617) 570-1000** 

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Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of "large accelerated filer," "accelerated filer," "smaller reporting company," and "emerging growth company" in Rule 12b-2 of the Exchange Act.

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| | | | |
|:---|:---|:---|:---|
| Large accelerated filer | ☐ | Accelerated filer | ☐ |
| Non-accelerated filer | ☒ | Smaller reporting company | ☒ |
|  |  | Emerging growth company | ☒ |

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If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐

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**STATEMENT OF INCORPORATION BY REFERENCE**

This Registration Statement on Form S-8 is being filed for the purpose of registering (i) an additional 2,246,397 shares of common stock, par value $0.0001 per share ("Common Stock"), of MBX Biosciences, Inc. (the "Registrant") to be issued under the Registrant's 2024 Stock Option and Incentive Plan (the "2024 Plan") and (ii) an additional 449,279 shares of Common Stock of the Registrant to be issued under the Registrant's 2024 Employee Stock Purchase Plan (the "2024 ESPP"), for which Registration Statements on Form S-8 (File No. 333-282106 and File No. 333-285846) relating to the same employee benefit plans are effective.

These additional shares are of the same class as other securities relating to the 2024 Plan and 2024 ESPP for which the Registrant's Registration Statements on Form S-8 (File No. 333-282106 and File No. 333-285846) filed with the Securities and Exchange Commission (the "Commission") on September 13, 2024 and March 17, 2025, respectively, are effective.

Pursuant to General Instruction E to Form S-8, the contents of the Registration Statements on Form S-8 (File No. 333-282106 and File No. 333-285846) filed with the Commission on September 13, 2024 and March 17, 2025, respectively, are incorporated by reference except to the extent supplemented, amended or superseded by the information set forth herein. Only those items of Form S-8 containing new information not contained in the earlier registration statements is presented herein.

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**Part II** 

**INFORMATION REQUIRED IN THE REGISTRATION STATEMENT** 

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| | |
|:---|:---|
| **Item 8.** | **Exhibits.**  |

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| | |
|:---|:---|
| **Exhibit<br>Number** | **Exhibit table** |
| &nbsp;&nbsp;&nbsp;&nbsp;4.1 | [<u>Fourth Amended and Restated Certificate of Incorporation of MBX Biosciences, Inc. (as currently in effect) (incorporated by reference to Exhibit 3.1 to the Registrant's Current Report on Form 8-K (File No. 001-42272) filed with the SEC on September 16, 2024).</u>](https://www.sec.gov/Archives/edgar/data/1776111/000119312524219621/d888081dex31.htm) |
| &nbsp;&nbsp;&nbsp;&nbsp;4.2 | [<u>Amended and Restated Bylaws of MBX Biosciences, Inc. (as currently in effect) (incorporated by reference to Exhibit 3.2 to the Registrant's Current Report on Form 8-K (File No. 001-42272) filed with the SEC on September 16, 2024).</u>](https://www.sec.gov/Archives/edgar/data/1776111/000119312524219621/d888081dex32.htm) |
| &nbsp;&nbsp;&nbsp;&nbsp;4.3 | [<u>Second Amended and Restated Investors' Rights Agreement among the Registrant and certain of its stockholders, dated August 2, 2024) (incorporated by reference to Exhibit 4.1 to the Registrant's Registration Statement on Form S-1 (File No. 333-281764) filed with the SEC on September 9, 2024).</u>](https://www.sec.gov/Archives/edgar/data/1776111/000119312524206227/d790774dex41.htm) |
| &nbsp;&nbsp;&nbsp;&nbsp;4.4 | [<u>Form of Common Stock Certificate (incorporated by reference to Exhibit 4.2 to the Registrant's Registration Statement on Form S-1 (File No. 333-281764) filed with the SEC on September 9, 2024</u>](https://www.sec.gov/Archives/edgar/data/1776111/000119312524206227/d790774dex42.htm) |
| &nbsp;&nbsp;&nbsp;&nbsp;4.5 | [<u>Description of Registrant's Securities (incorporated by reference to Exhibit 4.3 of the Registrant's Annual Report on Form 10-K (File No. 001-42272) filed with the Securities and Exchange Commission on March 17, 2025.</u>](https://www.sec.gov/Archives/edgar/data/1776111/000095017025039838/mbx-ex4_3.htm) |
| &nbsp;&nbsp;&nbsp;&nbsp;5.1\* | [<u>Opinion of Goodwin Procter LLP.</u>](mbx-ex5_1.htm) |
| 23.1\* | [<u>Consent of Ernst & Young LLP, Independent Registered Public Accounting Firm.</u>](mbx-ex23_1.htm) |
| 23.2\* | [<u>Consent of Goodwin Procter LLP (included in Exhibit 5.1).</u>](mbx-ex5_1.htm) |
| 24.1\* | [<u>Power of Attorney (included on signature page).</u>](#poa) |
| 99.1 | [<u>2024 Stock Option and Incentive Plan and forms of award agreements thereunder (incorporated by reference to Exhibit 10.2 to the Registrant's Registration Statement on Form S-1 (File No. 333-281764) filed with the SEC on September 9, 2024).</u>](https://www.sec.gov/Archives/edgar/data/1776111/000119312524211217/d790774dex102.htm) |
| 99.2 | [<u>2024 Employee Stock Purchase Plan(incorporated by reference to Exhibit 10.3 to the Registrant's Registration Statement on Form S-1 (File No. 333-281764) filed with the SEC on September 9, 2024).</u>](https://www.sec.gov/Archives/edgar/data/1776111/000119312524211217/d790774dex103.htm) |
| 107\* | [<u>Filing Fee Table.</u>](mbx-exfiling_fees.htm) |

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\* Filed herewith.

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**SIGNATURES** 

Pursuant to the requirements of the Securities Act, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-8 and has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Carmel, Indiana, on this 12th day of March, 2026.

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| | |
|:---|:---|
| &nbsp;&nbsp;&nbsp;**MBX Biosciences, Inc.** | &nbsp;&nbsp;&nbsp;**MBX Biosciences, Inc.** |
| By: | /s/ P. Kent Hawryluk |
|  | &nbsp;&nbsp;&nbsp;Name: P. Kent Hawryluk |
|  | &nbsp;&nbsp;&nbsp;Title: President and Chief Executive Officer |

---

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**POWER OF ATTORNEY AND SIGNATURES** 

KNOW ALL BY THESE PRESENT, that each individual whose signature appears below hereby constitutes and appoints each of P. Kent Hawryluk and Steven L. Hoerter, as such person's true and lawful attorney-in-fact and agent with full power of substitution and resubstitution, for such person in such person's name, place and stead, in any and all capacities, to sign any and all amendments (including post-effective amendments) to this Registration Statement, and to file the same, with all exhibits thereto, and all documents in connection therewith, with the Commission granting unto each said attorney-in-fact and agent full power and authority to do and perform each and every act and thing requisite and necessary to be done in and about the premises, as fully to all intents and purposes as such person might or could do in person, hereby ratifying and confirming all that any said attorney-in-fact and agent, or any substitute or substitutes of any of them, may lawfully do or cause to be done by virtue hereof.

Pursuant to the requirements of the Securities Act, this Registration Statement has been signed by the following person in the capacities and on the date indicated.

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| | | |
|:---|:---|:---|
| **NAME** | **TITLE** | **DATE** |
| /s/ P. Kent Hawryluk<br>P. Kent Hawryluk | &nbsp;&nbsp;&nbsp;President, Chief Executive Officer and Director<br>(Principal Executive Officer) | March 12, 2026 |
| /s/ Richard Bartram<br>Richard Bartram | &nbsp;&nbsp;&nbsp;Chief Financial Officer<br>(Principal Financial Officer and Principal Accounting Officer) | March 12, 2026<br>|
| /s/ Tiba Aynechi<br>Tiba Aynechi | &nbsp;&nbsp;&nbsp;Director | March 12, 2026<br>|
| /s/ Steven L. Hoerter<br>Steven L. Hoerter | &nbsp;&nbsp;&nbsp;Director | March 12, 2026<br>|
| /s/ Patrick Heron<br>Patrick Heron | &nbsp;&nbsp;&nbsp;Director | March 12, 2026<br>|
| /s/ Edward T. Mathers<br>Edward T. Mathers<br>| &nbsp;&nbsp;&nbsp;Director | March 12, 2026<br>|
| /s/ Ora Pescovitz<br>Ora Pescovitz<br>| &nbsp;&nbsp;&nbsp;Director | March 12, 2026<br>|
| /s/ Steven Ryder<br>Steven Ryder<br>| &nbsp;&nbsp;&nbsp;Director | March 12, 2026<br>|
| /s/ Laurie Stelzer<br>Laurie Stelzer | &nbsp;&nbsp;&nbsp;Director | March 12, 2026<br>|

---

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## Exhibit 5.1

**EXHIBIT 5.1**

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| | |
|:---|:---|
| &nbsp;&nbsp;![img84162877_0.jpg](img84162877_0.jpg) | &nbsp;&nbsp;Goodwin Procter LLP<br>100 Northern Avenue<br>Boston, MA 02210<br>goodwinlaw.com<br>+1 617 570 1000 |

---

March 12, 2026

MBX Biosciences, Inc.

11711 N. Meridian Street, Suite 300

Carmel, Indiana 46032

Re: <u>Securities Being Registered under Registration Statement on Form S-8</u>

We have acted as your counsel in connection with your filing of a Registration Statement on Form S-8 (the "Registration Statement") pursuant to the Securities Act of 1933, as amended (the "Securities Act"), on or about the date hereof relating to an aggregate of 2,695,676 shares (the "Shares") of Common Stock, par value $0.0001 per share ("Common Stock"), of MBX Biosciences, Inc., a Delaware corporation (the "Company"), that may be issued pursuant to the Company's 2024 Stock Option and Incentive Plan (the "2024 Plan") and the Company's 2024 Employee Stock Purchase Plan (the "2024 ESPP", together with the 2024 Plan, the "Plans").

We have reviewed such documents and made such examination of law as we have deemed appropriate to give the opinion set forth below. We have relied, without independent verification, on certificates of public officials and, as to matters of fact material to the opinion set forth below, on certificates of officers of the Company.

For purposes of the opinion set forth below, we have assumed that, at the time Shares are issued, the total number of then unissued Shares, when added to the number of shares of Common Stock issued, subscribed for, or otherwise committed to be issued, does not exceed the number of shares of Common Stock authorized by the Company's certificate of incorporation.

The opinion set forth below is limited to the Delaware General Corporation Law.

Based on the foregoing, we are of the opinion that the Shares have been duly authorized and, when delivered against payment therefor in accordance with the terms of the Plans, will be validly issued, fully paid and nonassessable.

This opinion letter and the opinion it contains shall be interpreted in accordance with the Core Opinion Principles as published in 74 *Business Lawyer* 815 (Summer 2019).

We hereby consent to the inclusion of this opinion as Exhibit 5.1 to the Registration Statement. In giving our consent, we do not admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations thereunder.

Very truly yours,

&nbsp;&nbsp;&nbsp;&nbsp; /s/ Goodwin Procter LLP

GOODWIN PROCTER LLP

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## Exhibit 23.1

**EXHIBIT 23.1**

**Consent of Independent Registered Public Accounting Firm**

We consent to the incorporation by reference in the Registration Statement (Form S-8) pertaining to the MBX Biosciences, Inc. 2024 Stock Option and Incentive Plan and MBX Biosciences, Inc. 2024 Employee Stock Purchase Plan of our report dated March 12, 2026, with respect to the financial statements of MBX Biosciences, Inc. included in its Annual Report (Form 10-K) for the year ended December 31, 2025, filed with the Securities and Exchange Commission.

/s/ Ernst & Young LLP

Indianapolis, Indiana

March 12, 2026

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## Ex-Filing

?xml version='1.0' encoding='ASCII'? EX-FILING FEES

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| |
|:---|
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; **Calculation of Filing Fee Tables**  |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; **S-8**  |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; **MBX Biosciences, Inc.**  |

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| | | | | | | | | |
|:---|:---|:---|:---|:---|:---|:---|:---|:---|
| | &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; **Security Type**  | &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; **Security Class Title**  | &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; **Fee Calculation Rule**  | &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; **Amount Registered**  | &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; **Proposed Maximum Offering Price Per Unit**  | &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; **Maximum Aggregate Offering Price**  | &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; **Fee Rate**  | &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; **Amount of Registration Fee**  |
| 1 | Equity | Common Stock, par value $0.0001 per share, reserved for issuance pursuant to the 2024 Stock Option and Incentive Plan | Other | 2246397 | $29.19 | $65572328.43 | 0.0001381 | $9055.54 |
| 2 | Equity | Common Stock, par value $0.0001 per share, reserved for issuance pursuant to the 2024 Employee Stock Purchase Plan | Other | 449279 | $24.81 | $11146611.99 | 0.0001381 | $1539.35 |
| Total Offering Amounts: | Total Offering Amounts: | Total Offering Amounts: | Total Offering Amounts: | Total Offering Amounts: |  | $76718940.42  |  | $10594.89  |
| Total Fee Offsets:  | Total Fee Offsets:  | Total Fee Offsets:  | Total Fee Offsets:  | Total Fee Offsets:  |  |  |  | $0.00  |
| Net Fee Due:  | Net Fee Due:  | Net Fee Due:  | Net Fee Due:  | Net Fee Due:  |  |  |  | $10594.89  |

---

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; **Offering Note** <br>

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <sup>1</sup> Pursuant to Rule 416 under the Securities Act of 1933, as amended, or the Securities Act, this Registration Statement on Form S-8, or the Registration Statement, shall also cover any additional shares of common stock, par value $0.0001 per share, or the Common Stock, of MBX Biosciences, Inc., or the Company, which become issuable by reason of any stock dividend, stock split, recapitalization or any other similar transaction effected without the receipt of consideration which results in an increase in the number of our outstanding shares of Common Stock. Pursuant to Rule 416(c) under the Securities Act, this Registration Statement shall also cover an indeterminate amount of interests to be offered or sold pursuant to the employee benefit plans described herein. Represents 2,246,397 additional shares of Common Stock authorized for issuance under the 2024 Stock Option and Incentive Plan, or the 2024 Plan, effective as of January 1, 2026, pursuant to an evergreen provision contained in the 2024 Plan. Pursuant to such provision, an additional number of shares will automatically be added to the shares authorized for issuance under the 2024 Plan on January 1 of each year. Shares available for issuance under the 2024 Plan were previously registered on registration statements on Form S-8 filed with the Securities and Exchange Commission ("SEC") on September 13, 2024 (File No. 333-282106) and March 17, 2025 (File No. 333-285846). Proposed maximum offering price per share estimated solely for the purpose of calculating the registration fee pursuant to Rules 457(c) and 457(h) of the Securities Act. The price per share and aggregate offering price are calculated on the basis of $29.19, the average of the high and low prices of the registrant's Common Stock as reported on the Nasdaq Global Select Market on March 9, 2026.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <sup>2</sup> Pursuant to Rule 416 under the Securities Act of 1933, as amended, or the Securities Act, this Registration Statement on Form S-8, or the Registration Statement, shall also cover any additional shares of common stock, par value $0.0001 per share, or the Common Stock, of MBX Biosciences, Inc., or the Company, which become issuable by reason of any stock dividend, stock split, recapitalization or any other similar transaction effected without the receipt of consideration which results in an increase in the number of our outstanding shares of Common Stock. Pursuant to Rule 416(c) under the Securities Act, this Registration Statement shall also cover an indeterminate amount of interests to be offered or sold pursuant to the employee benefit plans described herein. Represents 449,279 additional shares of Common Stock authorized for issuance under the 2024 Employee Stock Purchase Plan, or the ESPP, effective as of January 1, 2026, pursuant to an evergreen provision contained in the ESPP. Pursuant to such provision, an additional number of shares will automatically be added to the shares authorized for issuance under the ESPP on January 1 of each year. Shares available for issuance under the ESPP were previously registered on registration statements on Form S-8 filed with the SEC on September 13, 2024 (File No. 333-282106) and March 17, 2025 (File No. 333-285846). Proposed maximum offering price per share is estimated solely for the purpose of calculating the registration fee pursuant to Rules 457(c) and 457(h) of the Securities Act. The proposed maximum offering price per share and proposed maximum aggregate offering price are calculated on the basis of $24.81 per share, which is the average of the high and low prices of the registrant's Common Stock as reported on the Nasdaq Global Select Market on March 9, 2026, multiplied by 85%, which is the percentage of the price per share applicable to purchases under the ESPP.

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| | |
|:---|:---|
| | |
| **Rule 457(p)** | **Rule 457(p)** |
| Fee Offset Claims | N/A |
| Fee Offset Sources | N/A |

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