13D Filings
MBX BIOSCIENCES, INC.
MBX
Amendment
Ownership

4.80%

Total Shares

2,140,989

Issuer CIK

1776111

CUSIP

55287L101

Event Date

Sep 25, 2025

Accepted

Sep 30, 2025, 06:15 PM

Reporting Persons (6)
Joint Filing

This is a joint filing. The reported shares may overlap between reporting persons and should not be summed.

NameType% of ClassAggregateSole VotingShared Voting
Norwest Venture Partners XVI, LP
Partnership
4.80%2,136,33502,136,335
Genesis VC Partners XVI, LLC
Other
4.80%2,136,33502,136,335
NVP Associates, LLC
Other
4.80%2,136,33502,136,335
Jeffrey Crowe
Individual
4.80%2,136,33502,136,335
Jon Erik Kossow
Individual
4.80%2,136,33502,136,335
Tiba Aynechi
Individual
4.80%2,140,9894,6542,136,335
Disclosure Items (3)

Security Title

Common Stock, $0.0001 par value per share

Issuer Name

MBX BIOSCIENCES, INC.

Issuer Address

11711 N. Meridian Street, Suite 300, Carmel, IN, 46032

Percentage of Class

Rows 11 and 13 of each Reporting Person's cover page to this Schedule 13D/A set forth the aggregate number of shares of common stock and percentages of the shares of common stock beneficially owned by such Reporting Person and are incorporated by reference. The percentage set forth in each row 13 is based upon the sum of (i) 33,607,443 shares of common stock outstanding as of August 31, 2025, as reported in the Issuer's Registration Statement on Form S-1 filed with the Securities and Exchange Commission (the "SEC") on September 22, 2025; (ii) 11,108,055 shares of common stock issued in the Issuer's public offering of equity securities that closed on September 26, 2025; and (iii) with respect to Aynechi, 4,654 shares of common stock issuable upon the exercise of stock options within 60 days. Genesis XVI is the general partner of NVP XVI, NVP Associates is the managing member of Genesis XVI, Crowe and Kossow are Co-Chief Executive Officers of NVP Associates, and Aynechi is an officer of NVP Associates and a director of the Issuer. Each of Genesis XVI, NVP Associates, Crowe, Kossow and Aynechi, may be deemed to share voting and investment authority over the shares held by NVP XVI.

Number of Shares

Rows 7 through 10 of each Reporting Person's cover page to this Schedule 13D/A set forth the number of shares of common stock as to which such Reporting Person has the sole or shared power to vote or direct the vote and sole or shared power to dispose or to direct the disposition and are incorporated by reference.

Transactions

No transactions with respect to the securities of the Issuer have been effected during the past sixty days by any Reporting Person. The percentage ownership reported in this amendment reflect an increase in the number of outstanding shares of the Issuer.

Shareholders

No other person is known to have the right to receive or the power to direct the receipt of dividends from, or any proceeds from the sale of, the securities beneficially owned by any of the Reporting Persons.

Date of 5% Ownership

The Reporting Persons ceased to be the beneficial owners of more than five percent of the common stock on September 26, 2025.

Exhibit 99.1 Joint Filing Agreement (incorporated by reference to Exhibit A to the Reporting Persons' Schedule 13D filed with the SEC on September 23, 2024).