Deep Track Capital reports 3.64% MBX Biosciences (MBX) stake in 13G/A

Rhea-AI Filing Summary

MBX Biosciences, Inc. received an updated Schedule 13G/A (Amendment No. 2) from Deep Track Capital, LP, Deep Track Biotechnology Master Fund, Ltd., and David Kroin. The group reports beneficial ownership of 1,732,569 shares of common stock, representing 3.64% of the class as of June 30, 2026.

The reporting persons hold no sole voting or dispositive power, instead having shared voting and shared dispositive power over 1,732,569 shares. The percentage ownership is calculated using 47,597,536 shares outstanding as of May 4, 2026, as stated in MBX Biosciences’ Form 10-Q. The filing confirms ownership of 5% or less of the common stock.

Key Figures

Shares beneficially owned: 1,732,569 shares Percent of class: 3.64% Shares outstanding baseline: 47,597,536 shares +2 more

5 metrics

Shares beneficially owned 1,732,569 shares Common stock beneficially owned by the reporting persons as of June 30, 2026

Percent of class 3.64% Portion of MBX Biosciences common stock beneficially owned

Shares outstanding baseline 47,597,536 shares MBX Biosciences common stock outstanding as of May 4, 2026, per Form 10-Q

Shared voting power 1,732,569 shares Shares over which the reporting persons share voting power

Shared dispositive power 1,732,569 shares Shares over which the reporting persons share dispositive power

Key Terms

beneficially owned, shared voting power, shared dispositive power, parent holding company or control person, +1 more

5 terms

beneficially owned financial

"Amount beneficially owned: 1,732,569"

Beneficially owned describes securities or assets where a person has the economic rights and control—such as the right to receive dividends and to direct voting—even if legal title is held in another name. Think of it like having the keys and using a car that’s registered to someone else: you get the benefits and make decisions. Investors care because beneficial ownership reveals who truly controls value and voting power, affecting corporate decisions and takeover dynamics.

shared voting power financial

"Shared Voting Power 1,732,569.00"

Shared voting power occurs when two or more parties jointly have the right to vote or decide how a block of company shares is cast, like co-owners who must agree before moving a piece of furniture. Investors care because who controls voting rights affects board elections, major corporate decisions and takeover outcomes, and shared control can alter regulatory disclosures and the practical influence any holder has over a company’s direction and value.

shared dispositive power financial

"Shared Dispositive Power 1,732,569.00"

parent holding company or control person regulatory

"the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person"

Schedule 13G regulatory

"JOINT FILING STATEMENT PURSUANT TO RULE 13d-1(k)"

A Schedule 13G is a formal document that investors file with the government when they acquire a large ownership stake in a company, usually for investment purposes rather than control. It helps keep the public informed about who owns significant parts of a company's shares, which can influence how the company is managed and how investors make decisions. Filing this schedule is important for transparency and understanding the ownership landscape of publicly traded companies.

FAQ

What stake in MBX (MBX) does Deep Track Capital report in this Schedule 13G/A?

Deep Track Capital and related reporting persons report beneficial ownership of 1,732,569 MBX shares, equal to 3.64% of the common stock. This ownership reflects holdings as of June 30, 2026, based on the company’s reported shares outstanding.

How is the 3.64% ownership in MBX (MBX) calculated in the filing?

The 3.64% ownership is calculated using 47,597,536 MBX common shares outstanding as of May 4, 2026. That outstanding share figure comes from MBX Biosciences’ Form 10-Q filed with the SEC on May 7, 2026.

Who are the reporting persons in the MBX (MBX) Schedule 13G/A Amendment No. 2?

The reporting persons are Deep Track Capital, LP, Deep Track Biotechnology Master Fund, Ltd., and David Kroin. Deep Track Capital is a Delaware entity, the Master Fund is Cayman Islands–based, and David Kroin is a U.S. citizen and control person.

What voting and dispositive powers over MBX (MBX) shares are disclosed?

The reporting persons disclose zero sole voting and dispositive power and shared voting and shared dispositive power over 1,732,569 shares. This means decisions to vote or dispose of these MBX shares are made jointly, not individually, by the reporting group.

Does this MBX (MBX) Schedule 13G/A show ownership above or below 5%?

The filing explicitly states ownership of 5 percent or less of the class. With 3.64% beneficial ownership of MBX common stock, the Deep Track reporting group is below the 5% threshold that typically triggers Schedule 13D reporting requirements.

What role does David Kroin have in relation to Deep Track and MBX (MBX) holdings?

The document notes that Deep Track Capital, LP is the relevant entity for which David Kroin may be considered a control person. He signs as Managing Member of the General Partner of the Investment Adviser and as a Director of the Master Fund.

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

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Available on EDGAR 08/14/2026 - 08:28 AM Accepted by SEC EDGAR 08/14/2026 - 08:27 AM Learn about SEC filing dates

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 2)

MBX Biosciences, Inc.

(Name of Issuer)

Common Stock, $0.0001 par value per share

(Title of Class of Securities)

55287L101

(CUSIP Number)

06/30/2026

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

schemaVersion:

SCHEDULE 13G

CUSIP Number(s): 55287L101

1

Names of Reporting Persons

Deep Track Capital, LP

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 1,732,569.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 1,732,569.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

1,732,569.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

3.64 %

12

Type of Reporting Person (See Instructions)

IA, OO

SCHEDULE 13G

CUSIP Number(s): 55287L101

1

Names of Reporting Persons

Deep Track Biotechnology Master Fund, Ltd.

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

CAYMAN ISLANDS

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 1,732,569.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 1,732,569.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

1,732,569.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

3.64 %

12

Type of Reporting Person (See Instructions)

CO

SCHEDULE 13G

CUSIP Number(s): 55287L101

1

Names of Reporting Persons

David Kroin

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 1,732,569.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 1,732,569.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

1,732,569.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

3.64 %

12

Type of Reporting Person (See Instructions)

HC, IN

SCHEDULE 13G

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: (i) Deep Track Capital, LP (ii) Deep Track Biotechnology Master Fund, Ltd. (iii) David Kroin
(b)	Address or principal business office or, if none, residence: (i) 200 Greenwich Ave, 3rd Floor, Greenwich, CT 06830 (ii) c/o Walkers Corporate Limited, 190 Elgin Ave, George Town, KY1-9001, Cayman Islands (iii) c/o Deep Track Capital, LP, 200 Greenwich Ave, 3rd Floor, Greenwich, CT 06830
(c)	Citizenship: (i) Delaware (ii) Cayman Islands (iii) United States
(d)	Title of class of securities: Common Stock, $0.0001 par value 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: 1,732,569
(b)	Percent of class: 3.64%
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: 0
	(ii) Shared power to vote or to direct the vote: 1,732,569
	(iii) Sole power to dispose or to direct the disposition of: 0
	(iv) Shared power to dispose or to direct the disposition of: 1,732,569
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.
	If a parent holding company has filed this schedule, pursuant to Rule 13d-1(b)(ii)(G), so indicate under Item 3(g) and attach an exhibit stating the identity and the Item 3 classification of the relevant subsidiary. If a parent holding company has filed this schedule pursuant to Rule 13d-1(c) or Rule 13d-1(d), attach an exhibit stating the identification of the relevant subsidiary. Deep Track Capital, LP is the relevant entity for which David Kroin may be considered a control person.
Item 8.	Identification and Classification of Members of the Group.
	Not Applicable
Item 9.	Notice of Dissolution of Group.
	Not Applicable

Item 10.

Certifications:

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Deep Track Capital, LP

Signature:	/s/ David Kroin
Name/Title:	David Kroin, Managing Member of the General Partner of the Investment Adviser
Date:	08/14/2026

Deep Track Biotechnology Master Fund, Ltd.

Signature:	/s/ David Kroin
Name/Title:	David Kroin, Director
Date:	08/14/2026

David Kroin

Signature:	/s/ David Kroin
Name/Title:	David Kroin
Date:	08/14/2026

Exhibit Information

Item 4: Information with respect to the Reporting Persons' ownership of the Common Stock as of June 30, 2026, is incorporated by reference to items (5) - (9) and (11) of the cover page of the respective Reporting Person. The amount beneficially owned by each Reporting Person is determined based on 47,597,536 Common Stock outstanding as of May 4, 2026, according to the issuer's 10-Q filed with the SEC on May 7, 2026. JOINT FILING STATEMENT PURSUANT TO RULE 13d-1(k) The undersigned acknowledge and agree that the foregoing statement on SCHEDULE 13G, is filed on behalf of each of the undersigned and that all subsequent amendments to this statement on SCHEDULE 13G, shall be filed on behalf of each of the undersigned without the necessity of filing additional joint acquisition statements. The undersigned acknowledge that each shall be responsible for the timely filing of such amendments, and for the completeness and accuracy of the information concerning him or it contained therein, but shall not be responsible for the completeness and accuracy of the information concerning the others, except to the extent that he or it knows or has reason to believe that such information is inaccurate. Dated: August 14, 2026 Deep Track Capital, LP By: /s/ David Kroin David Kroin, Managing Member of the General Partner of the Investment Adviser Deep Track Biotechnology Master Fund, Ltd. By: /s/ David Kroin David Kroin, Director David Kroin By: /s/ David Kroin David Kroin