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MBX Biosciences, Inc. (MBX) awards CFO 130,000 options and 28,000 RSUs

(Neutral)
(Neutral)
Form Type
4

Rhea-AI Filing Summary

Smither John W reported acquisition or exercise transactions in this Form 4 filing.

MBX Biosciences, Inc. Chief Financial Officer John W. Smither received two equity awards on August 3, 2026. He was granted 28,000 restricted stock units that vest 25% each July 13, 2027–2030, and a stock option for 130,000 shares at $64.41 per share, vesting 25% on July 13, 2027 and monthly thereafter over 36 months, all subject to continued service.

Positive

  • None.

Negative

  • None.
Insider Smither John W
Role Chief Financial Officer
Type Security Shares Price Value
Grant/Award Stock option (right to buy) F2 130,000 $0.00 $0.00
Grant/Award Common Stock F1 28,000 $0.00 $0.00
Holdings After Transaction: Stock option (right to buy) — 130,000 shares (Direct); Common Stock — 28,000 shares (Direct)
Footnotes (2)
  1. F1. Represents the grant of restricted stock units ("RSUs"). 25% of the shares subject to the RSU grant will vest annually over four years, on each July 13, 2027, 2028, 2029 and 2030, subject to continued service on each such vesting date.
  2. F2. The options will vest and become exercisable with 25% of the shares subject to the award vesting on July 13, 2027 and the remainder vesting in 36 equal monthly installments thereafter, subject to continued service on each such vesting date.
RSU grant size 28,000 shares Restricted stock units granted to CFO on August 3, 2026
Option grant size 130,000 shares Stock option (right to buy) granted to CFO on August 3, 2026
Option exercise price $64.41 per share Conversion or exercise price of the 130,000-share stock option
Option expiration August 3, 2036 Expiration date of the CFO’s stock option award
RSU vesting schedule 25% annually 2027–2030 RSUs vest 25% on July 13, 2027, 2028, 2029 and 2030
Option vesting schedule 25% then 36 monthly installments 25% vests July 13, 2027; remaining 75% in 36 equal monthly installments
Common stock held after RSU grant 28,000 shares Direct common stock holdings reported following the RSU award
Options held after grant 130,000 options Total stock options reported following the option award
restricted stock units ("RSUs") financial
"Represents the grant of restricted stock units ("RSUs"). 25% of the shares"
Restricted stock units (RSUs) are a company promise to give an employee shares of stock (or cash equivalent) in the future, but only after certain conditions—usually staying with the company for a set time or hitting performance goals—are met. Investors watch RSUs because when they vest they increase the number of shares outstanding and can lead insiders to sell shares, affecting share price, company dilution and the true cost of employee pay.
Stock option (right to buy) financial
"security_title: "Stock option (right to buy)" for 130000.0000 shares"
vesting financial
"will vest and become exercisable with 25% of the shares subject to the award vesting"
Vesting is the process by which you earn full ownership of something, like company stock or a retirement benefit, over time. It’s like earning the right to keep a gift piece by piece the longer you stay with a company, making sure employees stay committed before they receive all the benefits.
underlying security financial
"underlying_security_title: "Common Stock" and underlying_security_shares"

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

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FAQ

What insider transactions did MBX (MBX) report for John W. Smither?

John W. Smither, MBX Biosciences’ CFO, received 28,000 restricted stock units and a stock option for 130,000 shares of common stock, both granted on August 3, 2026 as part of his equity compensation.

What are the terms of the RSU grant to the MBX (MBX) CFO?

The CFO’s RSU grant covers 28,000 shares. 25% of these RSUs vest each year on July 13, 2027, 2028, 2029 and 2030, provided he continues to serve through each vesting date.

How do the MBX (MBX) stock options granted to the CFO vest?

The CFO’s stock option for 130,000 shares vests with 25% on July 13, 2027, and the remaining 75% in 36 equal monthly installments thereafter, all contingent on continued service at each vesting date.

What is the exercise price and expiration date of the MBX (MBX) CFO’s options?

The CFO’s option has an exercise price of $64.41 per share and expires on August 3, 2036, giving him the right to buy up to 130,000 MBX Biosciences common shares before that date once vested.

Were the MBX (MBX) CFO’s equity awards granted under a Rule 10b5-1 plan?

The Rule 10b5-1 checkbox in this insider report was not marked, indicating these equity awards are not identified as being granted pursuant to a Rule 10b5-1 trading plan in this disclosure.
SEC Form 4
FORM 4UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940
OMB APPROVAL
OMB Number:3235-0287
Estimated average burden
hours per response:0.5
Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).
Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.
1. Name and Address of Reporting Person*
Smither John W

(Last)(First)(Middle)
11711 N. MERIDIAN STREET
SUITE 300

(Street)
CARMEL INDIANA 46032

(City)(State)(Zip)

UNITED STATES

(Country)
2. Issuer Name and Ticker or Trading Symbol
MBX Biosciences, Inc. [ MBX ]
5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
Director10% Owner
XOfficer (give title below)Other (specify below)
Chief Financial Officer
2a. Foreign Trading Symbol
3. Date of Earliest Transaction (Month/Day/Year)
08/03/2026
6. Individual or Joint/Group Filing (Check Applicable Line)
XForm filed by One Reporting Person
Form filed by More than One Reporting Person
4. If Amendment, Date of Original Filed (Month/Day/Year)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3) 2. Transaction Date (Month/Day/Year)2A. Deemed Execution Date, if any (Month/Day/Year)3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4)
CodeVAmount(A) or (D)Price
Common Stock08/03/2026A28,000(1)A$028,000D
Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (Month/Day/Year)3A. Deemed Execution Date, if any (Month/Day/Year)4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 6. Date Exercisable and Expiration Date (Month/Day/Year)7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4)
CodeV(A)(D)Date ExercisableExpiration DateTitleAmount or Number of Shares
Stock option (right to buy)$64.4108/03/2026A130,000 (2)08/03/2036Common Stock130,000$0130,000D
Explanation of Responses:
1. Represents the grant of restricted stock units ("RSUs"). 25% of the shares subject to the RSU grant will vest annually over four years, on each July 13, 2027, 2028, 2029 and 2030, subject to continued service on each such vesting date.
2. The options will vest and become exercisable with 25% of the shares subject to the award vesting on July 13, 2027 and the remainder vesting in 36 equal monthly installments thereafter, subject to continued service on each such vesting date.
Remarks:
Exhibit 24 - Power of Attorney
/s/ John W. Smither08/04/2026
** Signature of Reporting PersonDate
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.
* Form 4: SEC 1474 (03-26)