X0202 SCHEDULE 13D/A 0001056823 XXXXXXXX LIVE 3 Common Stock 04/24/2026 false 0001438472 59356Q108 MIAMI INTERNATIONAL HOLDINGS, INC.

7 ROSZEL ROAD FIFTH FLOOR, SUITE 1-A PRINCETON NJ 08540

Jay Kesslen 2128671176 470 Park Ave S 8th Floor South New York NY 07030 0001056823 N HORIZON KINETICS ASSET MANAGEMENT LLC WC N DE 11162809.00 11162809.00 11162809.00 N 12.2 IA 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 ("Managed Accounts") that hold securities of the Issuer. The following constitutes Amendment No. 3 to the schedule 13D filed by the undersigned. This Amendment No. 3 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 and Amendment No. 2 filed April 14, 2026. 0000088000 N Horizon Kinetics Holding Corp AF N DE 11162809.00 11162809.00 11162809.00 N 12.2 HC HKHC is the parent company to HKAM, a registered investment adviser. HKHC may be deemed to beneficially own the 11,162,809 shares beneficially owned by HKAM. HKHC has not entered into any separate transactions in the shares following the filing of Amendment No. 3 other than those listed under Schedule A, which were effectuated by HKAM. Common Stock MIAMI INTERNATIONAL HOLDINGS, INC. 7 ROSZEL ROAD FIFTH FLOOR, SUITE 1-A PRINCETON NJ 08540 Item 2 (a) 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 beneficially owned by Managed Accounts. On April 24, 2026, Eric Sites, who serves as a Managing Director of HKAM, was elected to the Board of Directors of the Issuer. 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 24, 2026, Eric Sites, who serves as a Managing Director of HKAM, was elected to the Board of Directors of the Issuer. Item 5 is hereby amended and restated in its entirety to read as follows: As of the close of business on April 27, 2026, HKAM beneficially owned 11,162,809 shares of common stock. The 11,162,809 shares beneficially owned represented 12.2% 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. On April 24, 2026, Eric Sites, who serves as a Managing Director of HKAM, was elected to the Board of Directors of the Issuer. HKAM's Sole Power to vote is 11,162,809 shares. 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. 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. N/A Exhibit 99.1 - 60 Day Trading History HORIZON KINETICS ASSET MANAGEMENT LLC /s/ Jay Kesslen 04/28/2026 Horizon Kinetics Holding Corp /s/ Jay Kesslen 04/28/2026