Horizon Kinetics (MIAX) accounts add 7,200 MIAX shares in open-market buy

Rhea-AI Filing Summary

MIAMI INTERNATIONAL HOLDINGS, INC. director Murray Stahl reported an indirect open‑market purchase of 7,200 shares of Common Stock of MIAX on March 4, 2026 at $43.38 per share. The shares are held in managed accounts of Horizon Kinetics Asset Management LLC, which now report 4,696,666 shares following the transaction.

The filing also lists fully vested options held directly by Mr. Stahl, with post‑transaction holdings of 7,500, 10,000, 14,331, and 2,500 options across several grants. The footnotes state that Mr. Stahl does not exercise investment discretion over the managed accounts and disclaims beneficial ownership except for any pecuniary interest.

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)

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	4,696,666(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	03/05/2026
	** 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?

MIAX reported an indirect open-market purchase of 7,200 shares of Common Stock at $43.38 per share on March 4, 2026, held in Horizon Kinetics Asset Management LLC managed accounts that now report 4,696,666 shares following the trade.

Who actually holds the MIAX shares bought in this Form 4 filing?

The 7,200 MIAX shares were purchased for managed accounts of Horizon Kinetics Asset Management LLC. Footnotes explain Murray Stahl does not exercise investment discretion over these accounts and disclaims beneficial ownership except for any pecuniary interest he may have.

How large is Horizon Kinetics’ reported MIAX position after the latest purchase?

After the March 4, 2026 purchase, Horizon Kinetics Asset Management LLC’s managed accounts report holding 4,696,666 MIAX common shares. The new buy of 7,200 shares slightly increased this indirect stake as disclosed in the Form 4 transaction details.

What price was paid for the MIAX shares in this insider transaction?

The reported open-market purchase price was $43.38 per MIAX common share. The Form 4 shows 7,200 shares acquired at this price on March 4, 2026, for managed accounts overseen by Horizon Kinetics Asset Management LLC.

What MIAX option holdings does Murray Stahl report in this Form 4?

The filing lists several fully vested MIAX option positions 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 rather than new option grants or exercises.

How does the Form 4 describe Murray Stahl’s role at Horizon Kinetics?

The Form 4 states Murray Stahl serves as Chairman, Chief Executive Officer and Chief Investment Officer of Horizon Kinetics Asset Management LLC, which manages the accounts holding MIAX securities. He disclaims beneficial ownership except to the extent of any pecuniary interest.