Miami International Holdings, Inc. SEC Filings

Miami International Holdings insider Edward Deitzel completed option exercises and share purchases in September 2025, increasing his direct holdings. On 09/09/2025 he exercised 62,500 nonqualified options with a $12 exercise price and acquired 62,500 common shares via that exercise. The same day 38,090 shares were surrendered to the company to satisfy tax withholding related to the net settlement of those exercises; this surrender is not a sale. On 09/10/2025 he exercised 16,666 incentive stock options at $12, and on 09/11/2025 he purchased 16,666 shares at $12. Following these transactions his reported beneficial ownership totaled 122,963 shares. All options exercised were fully vested.

Jayabalan Harish, EVP, CISO and CRO of Miami International Holdings, Inc. (MIAX), reported option exercises and resulting share ownership changes on 09/09/2025. He exercised 21,999 incentive stock options and 3,001 nonqualified stock options at a $12 exercise price, resulting in 25,000 shares acquired that day. The filing shows 72,384 shares beneficially owned after the first reported acquisition line and 75,385 after the second; a separate line records a net disposition of 1,980 shares at $37.30 representing shares surrendered to satisfy tax withholding on the net settlement of exercised options (not a sale). The reporting was signed by an attorney-in-fact on 09/11/2025.

Shelly Brown, EVP of Strategic Planning & Business Development at Miami International Holdings, Inc. (MIAX), reported a disposition of 16,283 shares of MIAX common stock on 09/10/2025 at a reported price of $36.81 per share. After the transaction, she beneficially owns 311,699 shares, held directly.

The filing explains these shares were surrendered to the company to satisfy tax withholding in connection with the net settlement of restricted stock awards and explicitly states this was not a sale by the reporting person. The Form 4 was submitted by an attorney-in-fact on behalf of the reporting person.

Miami International Holdings insider Shelly Brown reported a change in beneficial ownership on Form 4. The filing shows that on 08/26/2025 Ms. Brown had 11,047 shares of common stock surrendered to the company to satisfy tax withholding obligations related to the net settlement of restricted stock awards; the filing notes this was not a sale. Following the transaction her beneficial ownership is reported as 327,982 shares. The Form 4 was signed by an attorney-in-fact on 08/28/2025 and discloses Ms. Brown's role as EVP, Strategic Planning & BD.

Thomas P. Gallagher, Chairman & CEO and a director of Miami International Holdings, Inc. (MIAX), reported changes in his beneficial ownership on Form 4. On 08/26/2025 he disposed of 192,220 common shares under Code F at a price of $33.90 per share; the filing states these shares were surrendered to satisfy tax withholding related to net settlement of restricted stock awards and do not represent a sale. Following the reported transactions, Mr. Gallagher is shown as beneficially owning 1,848,274 shares indirectly through Gallagher Investments, LLC. The filing also corrects prior holdings to reflect an additional 2,000 shares purchased on 08/13/2025 and held jointly with his spouse. The form was signed by an attorney-in-fact on 08/28/2025.

Amendment No. 1 to Schedule 13D discloses updated ownership by Thomas P. Gallagher and Gallagher Investments LLC in Miami International Holdings, Inc. (MIAX) following the company's initial public offering. The Reporting Persons report beneficial ownership of 4,036,237 shares of common stock, representing 4.9% of the 80,799,866 shares outstanding as of August 26, 2025. Holdings include individually held shares, shares held by Gallagher Investments, and stock options exercisable within 60 days. Gallagher Investments surrendered 192,220 shares and $12.5 million in cash to satisfy tax withholding related to IPO-related vesting. The filing is described as a final amendment and an "exit filing" reflecting that the Reporting Persons ceased to beneficially own more than 5% as of August 26, 2025.

Thomas P. Gallagher and Gallagher Investments LLC reported beneficial ownership of 4,226,457 shares (5.1% of outstanding common stock) of Miami International Holdings, Inc. The filing shows Gallagher holds 573,963 shares directly, 12,000 jointly with his spouse, and options exercisable for 63,138 shares; Gallagher Investments holds 2,040,494 shares and options exercisable for 1,536,862 shares. Many shares resulted from conversions tied to the issuer's initial public offering and a small purchase of 12,000 IPO shares on August 14, 2025. Holdings are declared for investment with a 180-day lock-up and Gallagher serves as the issuer's Chairman and CEO, retaining voting and dispositive control over the shares reported.

Horizon Kinetics Asset Management LLC (HKAM) reported beneficial ownership of 8,679,747 shares of Miami International Holdings, Inc. common stock, representing 10.7% of the outstanding shares as of August 19, 2025. HKAM acquired these shares using approximately $65,000,000 of client assets and holds 8,400,880 shares plus warrants exercisable for 278,867 shares with various expiry dates through August 9, 2027. HKAM states the holdings are for investment purposes, may trade over time for client or regulatory reasons, and notes that Murray Stahl, HKAM’s Chairman and CIO, was appointed to the Issuer’s board on July 15, 2025.