Insider Purchase: Murray Stahl/Horizon Kinetics Increase MIAX Stake; Options and Warrants Disclosed

Rhea-AI Filing Summary

Murray Stahl and Horizon Kinetics Asset Management LLC reported insider transactions in Miami International Holdings, Inc. (MIAX). On 08/28/2025 a Form 4 shows a purchase of 34,470 shares of MIAX common stock at $36.10 per share. After the reported transaction, the filing shows beneficial ownership of 4,557,919 shares held indirectly by Horizon Kinetics. The filing also lists several vested stock options held directly by Mr. Stahl (totaling 43,131 options across multiple grant exercise prices and expirations) and multiple vested warrants held indirectly by Horizon Kinetics (totaling 137,656 warrants across different strikes and expiration dates). The filing clarifies Mr. Stahls roles at Horizon Kinetics and disclaims direct beneficial ownership except for any pecuniary interest.

Positive

• Insider purchase of 34,470 shares at $36.10 on 08/28/2025 indicating additional economic exposure
• Substantial reported indirect ownership of 4,557,919 shares by Horizon Kinetics, showing significant stakeholder interest
• Multiple vested options and warrants are disclosed, clarifying potential future exercise activity and ownership changes
• Filing corrects prior omissions (shares inadvertently excluded from Form 3) and discloses conversions to common stock

Negative

• None.

Insights

Securities Analyst

TL;DR: Director and affiliated 10% owner reported a purchase and sizable indirect holdings, plus vested options and warrants.

The Form 4 documents a 34,470-share open-market purchase at $36.10 by or on behalf of accounts affiliated with Horizon Kinetics on 08/28/2025, increasing reported indirect beneficial ownership to 4,557,919 shares. The filing distinguishes between directly held, fully vested options in Mr. Stahls name and indirectly held warrants held by Horizon Kinetics. For investors, the combination of an outright purchase and substantial indirect stake signals continued economic exposure from the asset manager; the presence of multiple vested derivative instruments creates potential future share issuance if exercised. This disclosure is routine but material to ownership structure and dilution considerations.

Corporate Governance Expert

TL;DR: Chairman/CEO of HKAM is reported as affiliated with a large indirect position and holds vested options; filing clarifies disclosure and disclaimers.

The filing provides clear role disclosure: Murray Stahl is Chairman, CEO, and CIO of Horizon Kinetics Asset Management LLC and the Form notes he does not exercise investment discretion for the managed accounts reported. The Form corrects prior omissions by including shares inadvertently excluded from an earlier Form 3 and identifies converted preferred and non-voting shares now reflected as common stock. The signature by an attorney-in-fact and the explanatory footnotes follow standard Section 16 protocols. This is a governance-appropriate, corrective and clarifying filing rather than an operational disclosure.

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

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).

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)
08/28/2025

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	08/28/2025		P		34,470	A	$36.1	4,557,919(1)(2)(3)	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(4)							08/13/2025	05/31/2031	Miami International Holdings Inc	2,500		2,500	D
OPTIONS	$16.14(4)							08/13/2025	07/31/2031	Miami International Holdings Inc	7,500		7,500	D
OPTIONS	$25.98(4)							08/13/2025	06/30/2032	Miami International Holdings Inc	10,000		10,000	D
OPTIONS	$19.84(4)							08/13/2025	03/26/2033	Miami International Holdings Inc	14,331		14,331	D
Warrants	$20.5(1)(5)							08/13/2025	11/15/2026	Miami International Holdings Inc	24,878		24,878	I	Horizon Kinetics Asset Management LLC
Warrants	$20.5(1)(5)							08/13/2025	02/05/2027	Miami International Holdings Inc	27,561		27,561	I	Horizon Kinetics Asset Management LLC
Warrants	$15(1)(5)							08/13/2025	04/08/2026	Miami International Holdings Inc	21,290		21,290	I	Horizon Kinetics Asset Management LLC
Warrants	$20.5(1)(5)							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. Includes Shares that were inadvertently excluded from the Form 3 filing made on August 13, 2025

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

5. 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 insider transaction was reported for MIAX on 08/28/2025?

The Form 4 reports a purchase of 34,470 shares of MIAMI INTERNATIONAL HOLDINGS, INC. common stock at $36.10 per share on 08/28/2025.

How many MIAX shares does Horizon Kinetics report beneficially owning?

The filing shows Horizon Kinetics Asset Management LLC indirectly beneficially owns 4,557,919 shares following the reported transaction.

Does Murray Stahl hold options or warrants in MIAX?

Yes. The Form 4 lists fully vested options held directly by Murray Stahl totaling 43,131 options across multiple exercise prices and expirations, and multiple warrants held indirectly by Horizon Kinetics totaling 137,656 warrants.

Did the Form 4 correct any prior filing errors?

Yes. The filing states it includes shares that were inadvertently excluded from a Form 3 filed on 08/13/2025 and notes converted Series B Preferred and Non-Voting Common shares that became common stock upon the IPO.

What relationship does Murray Stahl have to Horizon Kinetics and MIAX?

The filing identifies Murray Stahl as Chairman, Chief Executive Officer, and Chief Investment Officer of Horizon Kinetics; Horizon Kinetics is reported as a 10% owner of MIAX.