Indirect MIAX share buy via Horizon Kinetics for Miami International (MIAX)

Rhea-AI Filing Summary

MIAMI INTERNATIONAL HOLDINGS, INC. director Murray Stahl reported an indirect open‑market purchase of 7,200 shares of common stock at $43.08 per share through accounts managed by Horizon Kinetics Asset Management LLC. Those accounts held 4,633,842 shares of the issuer’s common stock after this transaction.

Stahl also reported fully vested option positions held directly, with post‑transaction holdings of 7,500 options, 10,000 options, 14,331 options, and 2,500 options as of March 5, 2026.

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)
03/05/2026

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	03/05/2026		P		7,200	A	$43.08	4,633,842(1)	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(2)							08/13/2025	07/31/2031	Miami International Holdings Inc	7,500		7,500	D
Options	$25.98(2)							08/13/2025	06/30/2032	Miami International Holdings Inc	10,000		10,000	D
Options	$19.84(2)							08/13/2025	03/26/2033	Miami International Holdings Inc	14,331		14,331	D
Options	$16.14(2)							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. 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 for Murray Stahl and Horizon Kinetics?

The filing reports an indirect open‑market purchase of 7,200 MIAX common shares at $43.08 per share. The shares are held in accounts managed by Horizon Kinetics Asset Management LLC, not personally by Stahl, and increase those managed accounts’ holdings in the issuer.

Who is shown as holding the MIAX shares after the 7,200‑share purchase?

After the transaction, managed accounts at Horizon Kinetics Asset Management LLC are shown holding 4,633,842 MIAX common shares. Murray Stahl is Chairman and CEO of Horizon Kinetics Asset Management but disclaims beneficial ownership except for any pecuniary interest described in the footnote.

How many MIAX common shares were bought and at what price in this Form 4?

The Form 4 shows a purchase of 7,200 MIAX common shares at $43.08 per share in an open‑market transaction. This buy is reported as an indirect transaction attributable to accounts managed by Horizon Kinetics Asset Management LLC, rather than a direct personal purchase by Stahl.

What MIAX option holdings for Murray Stahl are disclosed in this filing?

The filing lists fully vested options held directly by Murray Stahl with post‑transaction holdings of 7,500, 10,000, 14,331, and 2,500 options. These entries are reported as holdings, not new option grants or exercises, and relate to MIAX equity compensation already vested.

Does Murray Stahl have investment discretion over the MIAX shares in the managed accounts?

According to the footnote, Murray Stahl does not exercise investment discretion over MIAX securities held by the Horizon Kinetics managed accounts. He disclaims beneficial ownership of those securities, except to the extent of any pecuniary interest he may have in those accounts.

How is the nature of ownership described for the MIAX shares in this Form 4?

The 7,200 MIAX shares are reported as indirectly owned, with the nature of ownership described as Horizon Kinetics Asset Management LLC. Separately, the MIAX option positions are reported as directly owned by Murray Stahl and are identified as fully vested equity awards in the footnote.