Large MIAX holder Horizon Kinetics (MIAX) updates 13D and notes leader’s death

Rhea-AI Filing Summary

Horizon Kinetics Asset Management LLC filed Amendment No. 2 to its Schedule 13D on Miami International Holdings, Inc., reporting beneficial ownership of 11,061,399 shares of common stock, representing 12.1% of the outstanding class as of the close of business on April 9, 2026.

HKAM holds these shares in managed funds and accounts for investment purposes and may buy or sell additional shares in the ordinary course of business. The filing also notes that on April 7, 2026, Murray Stahl, who served as Chairman, Chief Executive Officer, and Chief Investment Officer of HKAM and was a Director of the issuer, passed away unexpectedly.

Insights

Governance & ownership analyst

Filing confirms a 12.1% stake and discloses the unexpected death of a key HKAM and issuer leader.

Horizon Kinetics Asset Management LLC reports beneficial ownership of 11,061,399 shares of Miami International Holdings, Inc., equal to 12.1% of the common stock as of the close of business on April 9, 2026. The stake is held across managed accounts, and HKAM states it acquired the position for investment purposes.

HKAM indicates it may increase or decrease its position in the ordinary course through open-market or private transactions, while disavowing beneficial ownership beyond its pecuniary interest. This keeps flexibility around position sizing and reflects a typical discretionary investment mandate for a large asset manager.

The filing also discloses that on April 7, 2026, Murray Stahl, Chairman, Chief Executive Officer, and Chief Investment Officer of HKAM and a Director of the issuer, passed away unexpectedly. This represents a material leadership loss for HKAM and removes a significant shareholder representative from the issuer’s board. The impact on strategy and governance will depend on subsequent appointments and disclosures.

Key Figures

Beneficial ownership: 11,061,399 shares Percent of class: 12.1% Sole voting power: 11,061,399 shares +1 more

4 metrics

Beneficial ownership 11,061,399 shares HKAM beneficially owned MIAX common stock as of close of business on April 9, 2026

Percent of class 12.1% Portion of MIAX outstanding common stock represented by HKAM’s 11,061,399 shares

Sole voting power 11,061,399 shares Shares of MIAX over which HKAM has sole voting power

Sole dispositive power 11,061,399 shares Shares of MIAX over which HKAM has sole dispositive power

Key Terms

beneficially owned, Schedule 13D, Sole Voting Power, Sole Dispositive Power, +2 more

6 terms

beneficially owned financial

"As of the close of business on April 9, 2026, HKAM beneficially owned 11,061,399 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.

Schedule 13D regulatory

"The following constitutes Amendment No. 2 to the filed by the undersigned (Amendment No. 2)."

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.

Sole Voting Power financial

"Number of Shares Beneficially Owned by Each Reporting Person With: 7 Sole Voting Power 11,061,399.00"

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

"9 Sole Dispositive Power 11,061,399.00"

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.

Managed Accounts financial

"with respect to the shares of common Stock of the Issuer ("Common Stock") beneficially owned by funds and accounts it manages ("Managed Accounts")."

Managed accounts are collections of investments owned by an individual or institution but run day-to-day by a professional who buys, sells and allocates assets according to an agreed plan. They matter to investors because they provide tailored oversight, active risk control and potential tax efficiency—like hiring a personal chef to manage your diet—while fees and the manager’s skill directly affect returns.

pecuniary interest financial

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

See more from StockTitan in Google Search and AI answers. Adds StockTitan as a preferred source · opens Google

Add on Google Not now

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 2)

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)

04/07/2026

(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 11,061,399.00
8	Shared Voting Power 0.00
9	Sole Dispositive Power 11,061,399.00
10	Shared Dispositive Power 0.00

11

Aggregate amount beneficially owned by each reporting person

11,061,399.00

12

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

13

Percent of class represented by amount in Row (11)

12.1 %

14

Type of Reporting Person (See Instructions)

IA

Comment for Type of Reporting Person:

Horizon Kinetics Asset Management LLC ("HKAM") is a Delaware limited liability company and a wholly owned subsidiary of Horizon Kinetics Holding Corporation ("HKHC"), a Delaware corporation, and manages funds and accounts that hold securities of the Issuer. HKAM is a wholly owned subsidiary of HKHC. The following constitutes Amendment No. 2 to the Schedule 13D filed by the undersigned (Amendment No. 2). This Amendment No. 2 amends, supplements and to the extent inconsistent with, supersedes the initial Schedule 13D filed with the Securities and Exchange Commission (the SEC) on August 14, 2025 as amended by Amendment No. 1 filed November 24, 2025. On April 7, 2026, Murray Stahl who served as Chairman, Chief Executive Officer, and Chief Investment Officer of HKAM, and Director of the Issuer passed away unexpectedly.

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 2.	Identity and Background
(a)	Item 2 is hereby amended and restated in its entirety to read as follows: This Schedule 13D is being filed by HKAM, a Delaware limited liability company and a wholly owned subsidiary of HKHC, a Delaware corporation, with respect to the shares of common Stock of the Issuer ("Common Stock") beneficially owned by funds and accounts it manages ("Managed Accounts"). On April 7, 2026, Murray Stahl who served as Chairman, Chief Executive Officer, and Chief Investment Officer of HKAM, and Director of the Issuer passed away unexpectedly.
Item 4.	Purpose of Transaction
	Item 4 is hereby amended and restated in its entirety to read as follows: 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 April 7, 2026, Murray Stahl who served as Chairman, Chief Executive Officer, and Chief Investment Officer of HKAM, and Director of the Issuer passed away unexpectedly.
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 April 9, 2026, HKAM beneficially owned 11,061,399 shares of common stock. The 11,061,399 shares beneficially owned represented 12.1% 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, as amended (the "Exchange Act"), or for any other purpose, and such beneficial ownership is expressly disclaimed, except to the extent of its pecuniary interest therein. On April 7, 2026, Murray Stahl who served as Chairman, Chief Executive Officer, and Chief Investment Officer of HKAM, and Director of the Issuer passed away unexpectedly.
(b)	HKAM's Sole Power to vote is 11,061,399 shares.
(c)	Except as set forth in Schedule A attached hereto as Exhibit 99-a, 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 99.1 - 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:	04/14/2026

FAQ

What ownership stake in MIAX does Horizon Kinetics Asset Management report?

Horizon Kinetics Asset Management LLC reports beneficial ownership of 11,061,399 shares of Miami International Holdings, Inc. common stock, representing 12.1% of the outstanding class as of the close of business on April 9, 2026, held across its managed accounts.

Why did Horizon Kinetics Asset Management file Amendment No. 2 to its Schedule 13D on MIAX?

The amendment updates information about Horizon Kinetics Asset Management LLC’s 13D position, confirming ownership of 11,061,399 MIAX shares and 12.1% of the class. It also revises identity, background, purpose of transaction, and interest sections, and discloses the unexpected passing of executive Murray Stahl.

What is Horizon Kinetics Asset Management’s stated purpose for holding MIAX shares?

Horizon Kinetics Asset Management LLC states it acquired MIAX common stock for investment purposes on behalf of its managed accounts. It may from time to time buy additional shares or sell shares through open-market or privately negotiated transactions in the ordinary course of its business activities.

How much voting power does Horizon Kinetics Asset Management have in MIAX?

Horizon Kinetics Asset Management reports sole voting power and sole dispositive power over 11,061,399 shares of Miami International Holdings, Inc. common stock, with no shared voting or dispositive power, giving it significant influence consistent with its 12.1% beneficial stake.

What leadership change related to MIAX is disclosed in this Horizon Kinetics filing?

The filing discloses that on April 7, 2026, Murray Stahl, who served as Chairman, Chief Executive Officer, and Chief Investment Officer of Horizon Kinetics Asset Management and was a Director of MIAX, passed away unexpectedly, representing a significant change in leadership and board composition.

Does Horizon Kinetics Asset Management disclaim any aspect of its beneficial ownership in MIAX?

Yes. Horizon Kinetics Asset Management states that neither the filing nor its contents constitute an admission that it is the beneficial owner of the MIAX common stock for purposes of Sections 13(d) or 16 of the Exchange Act, except to the extent of its pecuniary interest in the shares.