Horizon Kinetics (MIAX) reports 7.8% ownership and in-kind share distribution

Rhea-AI Filing Summary

Miami International Holdings, Inc. disclosed an amended Schedule 13D/A showing that Horizon Kinetics Asset Management LLC and its parent Horizon Kinetics Holding Corp beneficially own 7,400,316 shares of common stock, representing 7.8% of the company as of May 19, 2026.

HKAM holds sole voting and dispositive power over these shares, which are owned by client funds and accounts it manages. The position is held for investment purposes, and HKAM may buy or sell shares over time in the ordinary course of business. On May 19, 2026, HKAM distributed 4,084,261 shares in-kind on a pro rata basis, without consideration, to the beneficial owners of its managed accounts in response to client requests.

Insights

Equity ownership and governance analyst

Horizon Kinetics reports a 7.8% investment stake, with a large in-kind distribution to clients.

Horizon Kinetics Asset Management reports beneficial ownership of 7,400,316 shares of Miami International Holdings, equal to 7.8% of the common stock as of May 19, 2026. Voting and dispositive power rest with the adviser, but economic exposure belongs to underlying managed accounts.

The filing notes an in-kind, pro rata distribution of 4,084,261 shares to account holders without cash consideration, driven by client requests. This shifts shares from a concentrated reporting holder to multiple underlying investors while keeping Horizon’s remaining stake above 5%, so reporting obligations continue.

The adviser states the holdings are for investment purposes and that it may increase or reduce the position over time in open-market or private transactions. Subsequent ownership updates, if the stake moves materially from the current 7.8%, would appear in future beneficial ownership filings.

Key Figures

Beneficial ownership: 7,400,316 shares Ownership percentage: 7.8% In-kind distribution: 4,084,261 shares +2 more

5 metrics

Beneficial ownership 7,400,316 shares Common stock beneficially owned by HKAM as of May 19, 2026

Ownership percentage 7.8% Percent of MIAX common stock represented by 7,400,316 shares

In-kind distribution 4,084,261 shares Shares distributed pro rata to managed account clients on May 19, 2026

Sole voting power 7,400,316 shares Shares over which HKAM reports sole voting authority

Sole dispositive power 7,400,316 shares Shares over which HKAM reports sole dispositive authority

Key Terms

beneficially owned, sole voting power, sole dispositive power, in-kind, +2 more

6 terms

beneficially owned financial

"As of the close of business on May 19, 2026, HKAM beneficially owned 7,400,316 shares of common stock."

Beneficially owned describes securities or assets where a person has the economic rights and control—such as the right to receive dividends and to direct voting—even if legal title is held in another name. Think of it like having the keys and using a car that’s registered to someone else: you get the benefits and make decisions. Investors care because beneficial ownership reveals who truly controls value and voting power, affecting corporate decisions and takeover dynamics.

sole voting power financial

"Number of Shares Beneficially Owned by Each Reporting Person With: 7 Sole Voting Power 7,400,316.00"

Sole voting power is the exclusive right to cast votes attached to a shareholder’s stock without needing approval from anyone else. Like holding the only remote control for a TV, it lets that holder decide corporate matters such as board members, mergers, and policy changes, making it important to investors because it concentrates control and can strongly influence a company’s strategy and the value of its shares.

sole dispositive power financial

"Number of Shares Beneficially Owned by Each Reporting Person With: 9 Sole Dispositive Power 7,400,316.00"

Sole dispositive power is the exclusive legal authority to decide what happens to a security — for example, whether to sell, transfer, or retain shares — without needing anyone else’s permission. Investors care because it signals who truly controls the economic outcome of an investment: like holding the only key to a safe, the holder can realize gains or losses and may trigger regulatory reporting, insider rules, or influence over corporate ownership.

in-kind financial

"On May 19, 2026, HKAM distributed 4,084,261 shares in-kind on a pro rata basis without consideration to the beneficial owners of the Managed Accounts."

pecuniary interest financial

"such beneficial ownership is expressly disclaimed, except to the extent of its pecuniary interest therein."

Schedule 13D regulatory

"If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this"

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.

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SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 4)

MIAMI INTERNATIONAL HOLDINGS, INC.

(Name of Issuer)

Common Stock

(Title of Class of Securities)

59356Q108

(CUSIP Number)

Jay Kesslen
470 Park Ave S, 8th Fl S
New York, NY, 10016
646-867-1176

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

05/19/2026

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.

The information required on the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

schemaVersion:

SCHEDULE 13D

CUSIP Number(s): 59356Q108

1

Name of reporting person

HORIZON KINETICS ASSET MANAGEMENT LLC

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

WC

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 7,400,316.00
8	Shared Voting Power 0.00
9	Sole Dispositive Power 7,400,316.00
10	Shared Dispositive Power 0.00

11

Aggregate amount beneficially owned by each reporting person

7,400,316.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

7.8 %

14

Type of Reporting Person (See Instructions)

IA

Comment for Type of Reporting Person:

Horizon Kinetics Asset Management LLC ("HKAM"), a Delaware limited liability company and a wholly owned subsidiary of Horizon Kinetics Holding Corporation ("HKHC"), a Delaware corporation, manages funds and accounts ("Managed Accounts") that hold securities of the Issuer. The following constitutes Amendment No. 4 to the Schedule 13D filed by the undersigned. This Amendment No. 4 amends, supplements and to the extent inconsistent with, supersedes the initial Schedule 13D filed with the Securities and Exchange Commission on August 13, 2025, as amended by Amendment No. 1 filed November 24, 2025, Amendment No. 2 filed April 14, 2026, and Amendment No. 3 filed April 27, 2026.

SCHEDULE 13D

CUSIP Number(s): 59356Q108

1

Name of reporting person

Horizon Kinetics Holding Corp

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

AF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 7,400,316.00
8	Shared Voting Power 0.00
9	Sole Dispositive Power 7,400,316.00
10	Shared Dispositive Power 0.00

11

Aggregate amount beneficially owned by each reporting person

7,400,316.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

7.8 %

14

Type of Reporting Person (See Instructions)

HC

Comment for Type of Reporting Person:

HKHC is the parent company to HKAM, a registered investment adviser. HKHC may be deemed to beneficially own the 7,400,316 shares beneficially owned by HKAM. HKHC has not entered into any separate transactions in the shares other than those listed under Schedule A, and as described in Item 4 below, which were effectuated by HKAM.

SCHEDULE 13D

Item 1.	Security and Issuer
(a)	Title of Class of Securities: Common Stock
(b)	Name of Issuer: MIAMI INTERNATIONAL HOLDINGS, INC.
(c)	Address of Issuer's Principal Executive Offices: 7 ROSZEL ROAD, FIFTH FLOOR, SUITE 1-A, PRINCETON, NEW JERSEY , 08540.
Item 4.	Purpose of Transaction
	HKAM acquired the securities reported herein on behalf of the Managed Accounts for investment purposes. In the ordinary course of its business, HKAM intends to regularly review its equity interest in the Issuer and may, from time to time, acquire additional shares or other securities of the Issuer. While HKAM has no present intention to dispose of all or any portion of the shares beneficially owned by Managed Accounts, it may sell shares from time to time for a number of reasons, not limited to client requests, regulatory or investment limitations or other reasons. Any such sales of securities of the Issuer may be in the open market, privately negotiated transactions or otherwise. On May 19, 2026, HKAM distributed 4,084,261 shares in-kind on a pro rata basis without consideration to the beneficial owners of the Managed Accounts in response to client requests.
Item 5.	Interest in Securities of the Issuer
(a)	Item 5 is hereby amended and restated in its entirety to read as follows: As of the close of business on May 19, 2026, HKAM beneficially owned 7,400,316 shares of common stock. The 7,400,316 shares beneficially owned represented 7.8% of the outstanding shares of common stock. Neither the filing of this Schedule 13D nor any of its contents shall be deemed to constitute an admission that HKAM is the beneficial owner of the common stock referred to herein for purposes of Sections 13(d) and or 16 of the Securities Exchange Act of 1934, or for any other purpose, and such beneficial ownership is expressly disclaimed, except to the extent of its pecuniary interest therein.
(b)	HKAM's sole power to vote is 7,400,316 shares.
(c)	Except as set forth in this Schedule 13D, Item 4 above, and Schedule A attached hereto as Exhibit 99, HKAM has not effected any transaction in common stock in the past 60 days.
(d)	Except for Managed Accounts, who may have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, common stock, no other person is known by HKAM to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, any common stock that may be beneficially owned by HKAM.
(e)	n/a
Item 7.	Material to be Filed as Exhibits.
	Exhibit 99 - 60 Day Trading History

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

HORIZON KINETICS ASSET MANAGEMENT LLC

Signature:	/s/Jay Kesslen
Name/Title:	Jay Kesslen, General Counsel
Date:	05/21/2026

Horizon Kinetics Holding Corp

Signature:	/s/Jay Kesslen
Name/Title:	Jay Kesslen /General Counsel
Date:	05/21/2026

FAQ

What stake does Horizon Kinetics report in MIAX common stock?

Horizon Kinetics reports beneficial ownership of 7,400,316 MIAX common shares, representing 7.8% of the outstanding common stock as of May 19, 2026. These shares are held in managed accounts over which Horizon Kinetics has sole voting and dispositive power.

Who are the reporting persons in the MIAX Schedule 13D/A?

The reporting persons are Horizon Kinetics Asset Management LLC, a Delaware investment adviser, and its parent Horizon Kinetics Holding Corp. Both entities report beneficial ownership of the same 7,400,316 MIAX shares through client managed accounts they oversee.

What transaction did Horizon Kinetics disclose on May 19, 2026 for MIAX?

On May 19, 2026, Horizon Kinetics Asset Management distributed 4,084,261 MIAX shares in-kind on a pro rata basis without consideration to beneficial owners of its managed accounts. The distribution was made in response to client requests rather than a market sale.

Why does Horizon Kinetics hold MIAX shares according to the filing?

Horizon Kinetics states it acquired MIAX common stock for investment purposes on behalf of managed accounts. It intends to regularly review the equity interest and may from time to time buy additional shares or sell shares in open-market or privately negotiated transactions.

Does Horizon Kinetics plan to sell its MIAX position?

The filing says Horizon Kinetics has no present intention to dispose of all or any portion of the MIAX shares beneficially owned by managed accounts. However, it may sell shares from time to time for reasons such as client requests or investment limitations.

What voting power does Horizon Kinetics have over MIAX shares?

Horizon Kinetics Asset Management reports sole voting power and sole dispositive power over 7,400,316 MIAX common shares. No shared voting or shared dispositive power is reported, although economic benefits belong to the underlying managed account clients.