[Form 4] MIAMI INTERNATIONAL HOLDINGS, INC. Insider Trading Activity

Rhea-AI Filing Summary

Insider purchase and holdings disclosed. Murray Stahl and Horizon Kinetics Asset Management LLC reported acquisitions and existing derivative holdings in Miami International Holdings, Inc. (MIAX). On 09/26/2025 a purchase (code P) of Common Stock at $41.76 was reported, leaving 4,557,923 shares beneficially owned indirectly by Horizon Kinetics. The filing also lists vested, exercisable stock options awarded 08/13/2025 (totaling 34,831 options across four strike prices: $16.14, $25.98, $19.84) held directly, and multiple warrants held indirectly by Horizon Kinetics (totaling 137,636 warrants across various strikes and expiration dates). Murray Stahl is identified as Chairman, CEO, and CIO of HKAM and disclaims direct investment discretion over the managed accounts' holdings.

Positive

• Reported purchase of 4,557,923 common shares at $41.76 on 09/26/2025, increasing beneficial ownership indirectly via Horizon Kinetics
• Multiple vested and exercisable derivatives disclosed (options and warrants) with detailed strike prices and expiration dates
• Clear attribution of roles and disclaimers: Murray Stahl identified as Chairman/CEO/CIO of HKAM with a disclaimer of direct investment discretion

Negative

• None.

Insights

Securities Analyst

TL;DR: Significant indirect purchase by a 10% owner and multiple vested derivatives increase concentrated ownership.

The Form 4 shows a sizeable indirect acquisition of 4,557,923 common shares at $41.76 on 09/26/2025, filed by Horizon Kinetics Asset Management LLC, a reported 10% owner. Multiple vested options and exercisable warrants are detailed with specific strike prices and expirations, indicating both immediate and longer-term potential equity exposure. Reporting clarifies that Murray Stahl is an executive of HKAM but disclaims direct investment discretion over the managed accounts. For investors, the filing documents increased insider-aligned exposure without any statements of disposition or sales.

Corporate Governance Expert

TL;DR: Disclosure properly attributes indirect ownership and notes vested instruments; governance implications are standard.

The Form 4 attributes beneficial ownership to Horizon Kinetics and disclaims Murray Stahl's personal control over the specific managed-account positions, consistent with Section 16 reporting practices. The filing lists fully vested options and exercisable warrants, and itemizes conversion details for previously outstanding preferred and non-voting shares now reflected as common stock. Documentation is thorough with signature by attorney-in-fact, satisfying Form 4 formalities.

SEC Form 4

FORM 4

UNITED 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

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Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

1. Name and Address of Reporting Person^*

STAHL MURRAY

(Last) (First) (Middle)

470 PARK AVE S

8TH FLOOR SOUTH

(Street)

NEW YORK NY 10016

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
MIAMI INTERNATIONAL HOLDINGS, INC. [ MIAX ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

X	Director		10% Owner
	Officer (give title below)		Other (specify below)

3. Date of Earliest Transaction (Month/Day/Year)
09/26/2025

4. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

	Form filed by One Reporting Person
X	Form filed by More than One Reporting Person

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)
			Code	V	Amount	(A) or (D)	Price
Common Stock	09/26/2025		P		4	A	$41.76	4,557,923(1)(2)	I	Horizon Kinetics Asset Management LLC

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)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
OPTIONS	$16.14(3)							08/13/2025	05/31/2031	Miami International Holdings Inc	2,500		2,500	D
OPTIONS	$16.14(3)							08/13/2025	07/31/2031	Miami International Holdings Inc	7,500		7,500	D
OPTIONS	$25.98(3)							08/13/2025	06/30/2032	Miami International Holdings Inc	10,000		10,000	D
OPTIONS	$19.84(3)							08/13/2025	03/26/2033	Miami International Holdings Inc	14,331		14,331	D
Warrants	$20.5(1)(4)							08/13/2025	11/15/2026	Miami International Holdings Inc	24,878		24,878	I	Horizon Kinetics Asset Management LLC
Warrants	$20.5(1)(4)							08/13/2025	02/05/2027	Miami International Holdings Inc	27,561		27,561	I	Horizon Kinetics Asset Management LLC
Warrants	$15(1)(4)							08/13/2025	04/08/2026	Miami International Holdings Inc	21,290		21,290	I	Horizon Kinetics Asset Management LLC
Warrants	$20.5(1)(4)							08/13/2025	10/17/2026	Miami International Holdings Inc	38,927		38,927	I	Horizon Kinetics Asset Management LLC

1. Name and Address of Reporting Person^*

STAHL MURRAY

(Last) (First) (Middle)

470 PARK AVE S

8TH FLOOR SOUTH

(Street)

NEW YORK NY 10016

(City) (State) (Zip)

Relationship of Reporting Person(s) to Issuer

X	Director		10% Owner
	Officer (give title below)		Other (specify below)

1. Name and Address of Reporting Person^*

HORIZON KINETICS ASSET MANAGEMENT LLC

(Last) (First) (Middle)

470 PARK AVE S

8TH FLOOR SOUTH

(Street)

NEW YORK NY 10016

(City) (State) (Zip)

Relationship of Reporting Person(s) to Issuer

	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

Explanation of Responses:

1. Murray Stahl serves as Chairman, Chief Executive Officer, and Chief Investment Officer of Horizon Kinetics Asset Management LLC ("HKAM"), which manages funds and accounts (the "Managed Accounts") that hold securities of the Issuer. Mr. Stahl does not exercise investment discretion with respect to the securities of the Issuer that are beneficially owned by the Managed Accounts. Mr. Stahl disclaims beneficial ownership over the securities reported, except to the extent of his pecuniary interest therein, if any. The filing of this Form shall not be deemed an admission that the Mr. Stahl is the beneficial owner of such securities for purposes of Section 16 or any other purpose.

2. Includes 5,000 shares of Series B Preferred Stock that have been converted into Common Stock on a one-for-one basis upon the closing of the Company's initial public offering and which have no expiration date and 14,998 shares of Non-Voting Common Stock that have been converted into shares of Common Stock on a one-for-one basis upon the closing of the Company's IPO and which have no expiration date.

3. The Options given to Mr. Stahl are fully vested.

4. The Warrants are currently vested and presently exercisable until the expiration date show.

	/s/ Jay Kesslen, attorney-in-fact	09/30/2025
	** Signature of Reporting Person	Date
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.

FAQ

What did Murray Stahl and Horizon Kinetics report on Form 4 for MIAX?

They reported a purchase of Common Stock on 09/26/2025 at $41.76, resulting in 4,557,923 shares beneficially owned indirectly by Horizon Kinetics, and disclosed vested options and exercisable warrants.

How many common shares does Horizon Kinetics beneficially own after the reported transaction?

The Form 4 reports 4,557,923 shares beneficially owned following the 09/26/2025 transaction.

What options and warrants were disclosed in the filing?

The filing lists vested options (totaling 34,831 options across strikes of $16.14, $25.98, and $19.84) and 137,636 warrants across multiple strike prices and expiration dates, held directly or indirectly as specified.

Does Murray Stahl claim direct control over the reported securities?

No. The filing states Mr. Stahl does not exercise investment discretion over the securities held by the managed accounts and disclaims beneficial ownership except for any pecuniary interest.

Are the warrants exercisable now?

Yes. The filing states the listed warrants are currently vested and presently exercisable until their respective expiration dates.