7,200 MIAX shares bought by Horizon Kinetics for managed accounts

Rhea-AI Filing Summary

Miami International Holdings, Inc. reported an amended insider transaction involving accounts managed by Horizon Kinetics Asset Management LLC. On March 4, 2026, those managed accounts bought 7,200 shares of Common Stock of MIAX at $43.38 per share, recorded as indirect ownership through Horizon Kinetics.

Murray Stahl, a director of the company and Chairman, Chief Executive Officer, and Chief Investment Officer of Horizon Kinetics Asset Management, is associated with these accounts but does not exercise investment discretion over their MIAX securities and disclaims beneficial ownership except for any pecuniary interest. The amendment also updates fully vested option holdings reported directly in his name.

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

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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).

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^*

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)
03/04/2026

4. If Amendment, Date of Original Filed (Month/Day/Year)
03/05/2026

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	03/04/2026		P		7,200	A	$43.38	4,626,642(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	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
Options	$16.14(3)							08/13/2025	05/31/2031	Miami International Holdings Inc	2,500		2,500	D

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. This amendment corrects a previous filing that incorrectly listed the amount of securities beneficially owned.

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

	/s/ Jay Kesslen, attorney-in-fact	03/06/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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FAQ

What insider transaction did MIAX report in this amended Form 4/A?

The amended filing reports that accounts managed by Horizon Kinetics Asset Management bought 7,200 shares of MIAX Common Stock at $43.38 per share on March 4, 2026, and also updates fully vested option holdings reported for director Murray Stahl.

Who actually purchased the MIAX shares reported for Murray Stahl?

The shares were purchased by Managed Accounts overseen by Horizon Kinetics Asset Management LLC. Murray Stahl is an executive of Horizon Kinetics but does not exercise investment discretion over these MIAX securities and disclaims beneficial ownership except for any pecuniary interest he may have.

At what price and on what date were the MIAX shares bought?

The filing shows an open-market purchase of 7,200 MIAX Common Stock shares at $43.38 per share on March 4, 2026. The transaction is reported as indirect ownership through Horizon Kinetics Asset Management’s Managed Accounts rather than a direct personal purchase by Murray Stahl.

Why was an amended Form 4/A filed for MIAX?

The amendment states that it corrects a previous filing that had incorrectly listed the amount of securities beneficially owned. This updated Form 4/A revises the reported beneficial ownership figures while also detailing the recent share purchase and current option holdings for Murray Stahl.

What MIAX option holdings are reported for Murray Stahl in this Form 4/A?

The document lists several fully vested Options held directly by Murray Stahl, with updated post-transaction balances including 7,500, 10,000, 14,331, and 2,500 options. These entries are reported as holdings, not new option grants or exercises on the transaction date.

How is Murray Stahl’s beneficial ownership in MIAX described?

Murray Stahl is a director of MIAX and a senior executive at Horizon Kinetics Asset Management. The filing explains he does not exercise investment discretion over Managed Accounts holding MIAX securities and disclaims beneficial ownership of those securities except to the extent of any pecuniary interest.