MBX insider files Form 144 showing June option-related sale

MBX officer reported proposed sales of common stock under Form 144 related to stock option exercises and prior open-market dispositions.

Rhea-AI Filing Summary

MBX officer reported proposed sales of common stock under Form 144 related to stock option exercises and prior open-market dispositions. The filing lists multiple sales and proposed sale activity, including individual transactions on 03/16/2026, 03/25/2026, 04/22/2026, and several dates in May and June 2026.

Insights

Corporate Governance Analyst

Insider resale disclosures show routine liquidity events, not a change in control.

The filing lists multiple sales by Richard B. Bartram and a proposed sale via stock option exercise on 06/09/2026. These entries are routine reseller disclosures required when affiliates propose sales.

Cashflow treatment is shown as Cash for the June exercise; subsequent filings may report settlement details. The transactions should be read as disclosure of planned or completed dispositions, not an operational update.

Key Figures

Proposed exercise sale: 10,833 shares Sale on 05/11/2026: 22,500 shares Sale on 05/08/2026: 10,000 shares +3 more

6 metrics

Proposed exercise sale 10,833 shares listed with Fidelity Brokerage Services LLC on 06/09/2026 as stock option exercise

Sale on 05/11/2026 22,500 shares gross proceeds <money>$991,901.00</money>

Sale on 05/08/2026 10,000 shares gross proceeds <money>$379,562.50</money>

Sale on 04/22/2026 10,423 shares gross proceeds <money>$341,377.72</money>

Sale on 05/13/2026 15,000 shares gross proceeds <money>$554,295.50</money>

Sale on 03/16/2026 10,000 shares gross proceeds <money>$300,471.00</money>

Key Terms

Form 144, Stock Option Exercise, Cash, Fidelity Brokerage Services LLC

4 terms

Form 144 regulatory

"144: Securities To Be Sold"

Form 144 is a document that investors must file with the government when they plan to sell a large number of shares of a company's stock. It helps ensure transparency so everyone knows how many shares are being sold and when, which can impact the stock's price.

Stock Option Exercise financial

"Common | 06/09/2026 | Stock Option Exercise"

A stock option exercise is the act of using a previously granted right to buy shares of a company's stock at a specific, predetermined price by paying that price and receiving the shares. It matters to investors because exercising changes who owns the shares (which can dilute existing ownership), can trigger taxable events and shift potential gains or losses, and affects voting power and the company’s outstanding share count—like turning a voucher into an actual product that becomes part of circulating supply.

Cash financial

"10833 | 06/09/2026 | Cash"

Fidelity Brokerage Services LLC other

"Fidelity Brokerage Services LLC 900 Salem Street Smithfield"

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What does MBX Form 144 filing mean?

A Form 144 is a notice of proposed sale by an affiliate; it reports planned or recent dispositions of restricted or control securities. This filing lists multiple sales by Richard B. Bartram and a proposed stock option exercise sale dated 06/09/2026.

How many MBX shares were sold by the insider in May 2026?

The filing lists May 2026 transactions including 5,000 shares on 05/01/2026, 10,000 on 05/07/2026, 10,000 on 05/08/2026, 22,500 on 05/11/2026, and 15,000 on 05/13/2026. Each row shows share count and gross proceeds.

Who is the selling person in the MBX Form 144?

The selling person named is Richard B. Bartram with an address in Carmel, Indiana. The filing also lists Fidelity Brokerage Services LLC as the broker for a proposed sale related to a stock option exercise on 06/09/2026.

Does the Form 144 show sale proceeds for each transaction?

Yes; individual transactions include gross proceeds figures, for example $991,901.00 for 22,500 shares sold on 05/11/2026 and $379,562.50 for 10,000 shares on 05/08/2026. Each line pairs shares and proceeds.

Is the June 9, 2026 sale an exercise or open-market sale?

The June 9, 2026 entry is labeled Stock Option Exercise and shows Cash as the cashflow method, indicating the sale is tied to an option exercise and cash settlement through Fidelity Brokerage Services LLC.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Accepted by SEC EDGAR 06/09/2026 - 04:38 PM Learn about SEC filing dates

Form 144 Filer Information	UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Form 144 NOTICE OF PROPOSED SALE OF SECURITIES PURSUANT TO RULE 144 UNDER THE SECURITIES ACT OF 1933
FORM 144

144: Filer Information

Filer CIK	0001723729
Filer CCC	XXXXXXXX
Is this a LIVE or TEST Filing?	LIVE TEST
Submission Contact Information
Name
Phone
E-Mail Address

144: Issuer Information

Name of Issuer	MBX Biosciences, Inc.
SEC File Number	001-42272
Address of Issuer	11711 N. MERIDIAN STREET SUITE 300 CARMEL INDIANA 46032
Phone	3179893100
Name of Person for Whose Account the Securities are To Be Sold	Bartram Richard
See the definition of "person" in paragraph (a) of Rule 144. Information is to be given not only as to the person for whose account the securities are to be sold but also as to all other persons included in that definition. In addition, information shall be given as to sales by all persons whose sales are required by paragraph (e) of Rule 144 to be aggregated with sales for the account of the person filing this notice.
Relationship to Issuer	Former Officer

144: Securities Information

Title of the Class of Securities To Be Sold	Name and Address of the Broker	Number of Shares or Other Units To Be Sold	Aggregate Market Value	Number of Shares or Other Units Outstanding	Approximate Date of Sale	Name the Securities Exchange
Common	Fidelity Brokerage Services LLC 900 Salem Street Smithfield RI 02917	10833	321273.40	47597536	06/09/2026	NASDAQ

Furnish the following information with respect to the acquisition of the securities to be sold and with respect to the payment of all or any part of the purchase price or other consideration therefor:

144: Securities To Be Sold

Title of the Class	Date you Acquired	Nature of Acquisition Transaction	Name of Person from Whom Acquired	Is this a Gift?	Date Donor Acquired	Amount of Securities Acquired	Date of Payment	Nature of Payment *
Common	06/09/2026	Stock Option Exercise	Issuer			10833	06/09/2026	Cash

* If the securities were purchased and full payment therefor was not made in cash at the time of purchase, explain in the table or in a note thereto the nature of the consideration given. If the consideration consisted of any note or other obligation, or if payment was made in installments describe the arrangement and state when the note or other obligation was discharged in full or the last installment paid.

Furnish the following information as to all securities of the issuer sold during the past 3 months by the person for whose account the securities are to be sold.

144: Securities Sold During The Past 3 Months

Name and Address of Seller	Title of Securities Sold	Date of Sale	Amount of Securities Sold	Gross Proceeds
Richard B. Bartram 11711 N. Meridian Street, Suite 300 Carmel IN 46032	Common	03/16/2026	10000	300471.00
Richard B. Bartram 11711 N. Meridian Street, Suite 300 Carmel IN 46032	Common	03/25/2026	1061	30217.49
Richard B. Bartram 11711 N. Meridian Street, Suite 300 Carmel IN 46032	Common	04/22/2026	10423	341377.72
Richard B. Bartram 11711 N. Meridian Street, Suite 300 Carmel IN 46032	Common	05/01/2026	5000	159000.00
Richard B. Bartram 11711 N. Meridian Street Suite 300 Carmel IN 46032	Common	05/07/2026	10000	322050.00
Richard B. Bartram 11711 N. Meridian Street Suite 300 Carmel IN 46032	Common	05/08/2026	10000	379562.50
Richard B. Bartram 11711 N. Meridian Street Suite 300 Carmel IN 46032	Common	05/11/2026	22500	991901.00
Richard B. Bartram 11711 N. Meridian Street Suite 300 Carmel IN 46032	Common	05/13/2026	15000	554295.50

144: Remarks and Signature

Remarks
Date of Notice	06/09/2026
ATTENTION:
The person for whose account the securities to which this notice relates are to be sold hereby represents by signing this notice that he does not know any material adverse information in regard to the current and prospective operations of the Issuer of the securities to be sold which has not been publicly disclosed. If such person has adopted a written trading plan or given trading instructions to satisfy Rule 10b5-1 under the Exchange Act, by signing the form and indicating the date that the plan was adopted or the instruction given, that person makes such representation as of the plan adoption or instruction date.
Signature	/s/ Gerardo Ibarra-Munoz, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Richard B. Bartram
ATTENTION: Intentional misstatements or omission of facts constitute Federal Criminal Violations (See 18 U.S.C. 1001)