| Item 1. | |
| (a) | Name of issuer:
MBX Biosciences, Inc. |
| (b) | Address of issuer's principal executive offices:
11711 N. Meridian Street, Suite 300, Carmel, Indiana 46032 |
| Item 2. | |
| (a) | Name of person filing:
P. Kent Hawryluk (the "Reporting Person"). |
| (b) | Address or principal business office or, if none, residence:
The business address of the Reporting Person is c/o MBX Biosciences, Inc., 11711 N. Meridian Street, Suite 300, Carmel, Indiana 46032. |
| (c) | Citizenship:
The Reporting Person is a citizen of the United States of America. |
| (d) | Title of class of securities:
Common Stock, par value $0.0001 per share |
| (e) | CUSIP No.:
55287L101 |
| Item 3. | If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a: |
| (a) |  Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
|
| (b) | Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
|
| (c) | Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
|
| (d) | Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
|
| (e) | An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
|
| (f) | An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
|
| (g) | A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
|
| (h) | A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
|
| (i) | A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
|
| (j) | A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J),
please specify the type of institution:
|
| (k) | Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
|
| | |
| Item 4. | Ownership |
| (a) | Amount beneficially owned:
The Reporting Person may be deemed to be the beneficial owner of 1,995,759 shares of Common Stock, which includes: (i) 481,397 shares of Common Stock, $0.0001 par value per share (the "Common Stock") held directly by the Reporting Person, (ii) 1,066,085 shares of Common Stock issuable upon exercise of stock options exercisable within 60 days of September 30, 2025 held directly by the Reporting Person, and (iii) 448,277 shares of Common Stock held by the P. Kent Hawryluk Revocable Trust dated January 25, 2011, of which the Reporting Person serves as trustee.
The percentage of class was calculated based on (i) 44,902,302 shares of Common Stock outstanding as of November 3, 2025, as disclosed in the Issuer's Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission on November 6, 2025, plus (ii) an aggregate of 1,066,085 shares of Common Stock issuable upon exercise of stock options exercisable within 60 days of September 30, 2025, which are deemed outstanding pursuant to SEC Rule 13-3(d)(1)(i) only for purposes of computing the percentage ownership of the Reporting Person. |
| (b) | Percent of class:
4.3% |
| (c) | Number of shares as to which the person has:
|
| | (i) Sole power to vote or to direct the vote:
1,995,759
|
| | (ii) Shared power to vote or to direct the vote:
0
|
| | (iii) Sole power to dispose or to direct the disposition of:
1,995,759
|
| | (iv) Shared power to dispose or to direct the disposition of:
0
|
| Item 5. | Ownership of 5 Percent or Less of a Class. |
| | 
Ownership of 5 percent or less of a class
|
| Item 6. | Ownership of more than 5 Percent on Behalf of Another Person. |
| |
Not Applicable
|
| Item 7. | Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person. |
| |
Not Applicable
|
| Item 8. | Identification and Classification of Members of the Group. |
| |
Not Applicable
|
| Item 9. | Notice of Dissolution of Group. |
| |
Not Applicable
|