Horizon Kinetics restructures MIAX share holdings

Horizon Kinetics Asset Management LLC (HKAM), a more than 10% owner of MIAMI INTERNATIONAL HOLDINGS, INC., reported an internal restructuring of its indirect holdings of common stock.

Rhea-AI Filing Summary

Horizon Kinetics Asset Management LLC (HKAM), a more than 10% owner of MIAMI INTERNATIONAL HOLDINGS, INC., reported an internal restructuring of its indirect holdings of common stock. The filing shows a non-cash, in-kind pro rata distribution that reduced HKAM’s pecuniary interest in certain shares.

The change reflects a reduction of 2,455,744 shares that were distributed in-kind without consideration, plus 7,200 shares in an account where HKAM no longer has a pecuniary interest. Following these changes, HKAM reports indirect ownership of 2,170,898 shares in this Form 4 and separately reports beneficial ownership of 7,400,316 shares, or 7.8 percent of the issuer’s outstanding shares, in an amended Schedule 13D.

Insider Trade Summary

Other: 2,455,744 shares

Other 1 txn

Insider HORIZON KINETICS ASSET MANAGEMENT LLC

Role 10% Owner

Type	Security	Shares	Price	Value
Other	Common Stock	2,455,744	$0.00	$0.00

Holdings After Transaction: Common Stock — 2,170,898 shares (Indirect, Horizon Kinetics Asset Management LLC)

Footnotes (3)

1. F1. On May 21, 2026, Horizon Kinetics Asset Management LLC ("HKAM") filed an amendment to its Schedule 13D wherein it reported beneficial ownership of 7,400,316 shares or 7.8 percent of the outstanding shares of the Issuer. The extent of HKAM's pecuniary interest in the shares reported in the Schedule 13D are disclosed herein.
2. F2. The change represents a reduction of 2,455,744 shares that were distributed in-kind on a pro rata basis, without consideration.
3. F3. This amount reflects a reduction of 7,200 shares that were held in an account for which the Reporting Person no longer has a pecuniary interest.

Key Figures

In-kind distribution: 2,455,744 shares Additional reduction: 7,200 shares Indirect holdings after transaction: 2,170,898 shares +2 more

5 metrics

In-kind distribution 2,455,744 shares Shares distributed in-kind on a pro rata basis without consideration

Additional reduction 7,200 shares Shares in an account where Horizon Kinetics no longer has pecuniary interest

Indirect holdings after transaction 2,170,898 shares MIAX common stock indirectly owned following the reported restructuring

Beneficial ownership 7,400,316 shares Shares beneficially owned by Horizon Kinetics per amended Schedule 13D

Ownership percentage 7.8 percent Share of MIAX outstanding shares reported as beneficially owned

Key Terms

Schedule 13D, beneficial ownership, in-kind, pro rata basis, +1 more

5 terms

Schedule 13D regulatory

"filed an amendment to its Schedule 13D wherein it reported beneficial ownership"

A Schedule 13D is a legal document that investors file with regulators when they buy a large enough stake in a company to potentially influence its management or decisions. It provides details about the investor’s intention, ownership stake, and plans, helping other investors understand who is gaining control and what their motives might be.

beneficial ownership financial

"wherein it reported beneficial ownership of 7,400,316 shares or 7.8 percent"

Beneficial ownership means the person or entity that actually enjoys the benefits of owning shares or other assets — such as receiving dividends, voting rights, or price gains — even if the legal title is held in another name. For investors it matters because knowing who truly controls and profits from a company reveals who can influence decisions, exposes potential conflicts of interest or hidden concentration of power, and affects transparency and risk in the stock.

in-kind financial

"shares that were distributed in-kind on a pro rata basis, without consideration"

pro rata basis financial

"distributed in-kind on a pro rata basis, without consideration"

A "pro rata basis" means dividing or distributing something proportionally according to each person's share or interest. For example, if a group shares costs or profits, each person receives or pays a portion that reflects their contribution or ownership percentage. This method ensures fairness by allocating resources in line with individual stakes, which is important for investors to understand how gains, losses, or costs are fairly shared.

pecuniary interest financial

"shares that were held in an account for which the Reporting Person no longer has a pecuniary interest"

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What did Horizon Kinetics Asset Management report in this MIAX Form 4?

Horizon Kinetics Asset Management LLC reported an internal restructuring of its MIAX common stock holdings. The filing records a non-cash, in-kind distribution that reduced its pecuniary interest in certain shares while maintaining a substantial indirect and beneficial ownership position overall.

How many MIAX shares were reduced in Horizon Kinetics’ restructuring?

The restructuring reflects a reduction of 2,455,744 MIAX shares through an in-kind, pro rata distribution. An additional 7,200 shares were removed from its reported interest because they were held in an account where Horizon Kinetics no longer has a pecuniary interest.

How many MIAX shares does Horizon Kinetics report holding after this Form 4 transaction?

After the transaction, Horizon Kinetics reports indirect ownership of 2,170,898 MIAX common shares in this Form 4. These shares are held indirectly, with Horizon Kinetics Asset Management LLC listed as the nature of ownership for the reported position.

What is Horizon Kinetics’ overall beneficial ownership stake in MIAX?

Horizon Kinetics reported beneficial ownership of 7,400,316 MIAX shares in an amended Schedule 13D. This beneficial ownership represents 7.8 percent of MIAMI INTERNATIONAL HOLDINGS, INC.’s outstanding shares as disclosed in the referenced Schedule 13D amendment.

Was the Horizon Kinetics MIAX share change a cash sale or purchase?

The change was not a cash sale or purchase of MIAX shares. The Form 4 indicates a non-cash, in-kind pro rata distribution made without consideration, reflecting an internal restructuring rather than an open-market trade in the company’s stock.

How is Horizon Kinetics’ MIAX ownership characterized in this Form 4 filing?

The MIAX shares in this Form 4 are reported as indirect ownership by Horizon Kinetics Asset Management LLC. The nature of ownership is listed under Horizon Kinetics Asset Management LLC, indicating the shares are held through an entity rather than directly by an individual insider.

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Accepted by SEC EDGAR 05/21/2026 - 05:21 PM EDT Learn about SEC filing dates

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

X

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^*

HORIZON KINETICS ASSET MANAGEMENT LLC

(Last) (First) (Middle)

470 PARK AVE S

8TH FLOOR SOUTH

(Street)

NEW YORK NEW YORK 10016

(City) (State) (Zip)

UNITED STATES

(Country)

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

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

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

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
05/19/2026

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

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

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

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	05/19/2026		J		2,455,744	D	$0	2,170,898(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

Explanation of Responses:

1. On May 21, 2026, Horizon Kinetics Asset Management LLC ("HKAM") filed an amendment to its Schedule 13D wherein it reported beneficial ownership of 7,400,316 shares or 7.8 percent of the outstanding shares of the Issuer. The extent of HKAM's pecuniary interest in the shares reported in the Schedule 13D are disclosed herein.

2. The change represents a reduction of 2,455,744 shares that were distributed in-kind on a pro rata basis, without consideration.

3. This amount reflects a reduction of 7,200 shares that were held in an account for which the Reporting Person no longer has a pecuniary interest.

Remarks:

Murray Stahl previously served as a Director of the Issuer and the Chairman, Chief Executive Officer and Chief Investment Officer of Horizon Kinetics Asset Management LLC ("HKAM") until his passing on April 7, 2026. On April 24, 2026, Eric Sites, who serves as a Managing Director of HKAM, was appointed to the Issuer's Board of Directors. Mr. Sites does not exercise investment discretion on behalf of HKAM with respect to the securities of the Issuer and is not deemed to beneficially own the securities reported herein. The extent of Mr. Sites' pecuniary interest in the securities of the Issuer are reported separately in his own filings.

	/s/ Jay Kesslen, attorney-in-fact	05/21/2026
	** 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.
* Form 4: SEC 1474 (03-26)