Sec Form 3 Filing - Teekell Judson Gray @ MIAMI INTERNATIONAL HOLDINGS, INC. - 2025-08-13

FORM 3 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

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, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Teekell Judson Gray 2. Issuer Name and Ticker or Trading Symbol MIAMI INTERNATIONAL HOLDINGS, INC. [ MIAX] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O MIAMI INTERNATIONAL HOLDINGS, INC., 7 ROSZEL ROAD, SUITE 1A 3. Date of Earliest Transaction (MM/DD/YY) 08/13/2025 (Street) PRINCETON, NJ08540 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 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 1,096 D Common Stock 18,414 ( 1 ) I By estate of Byrum W. Teekell Common Stock 57,219 ( 2 ) I By Teekell Oil & Gas, Inc. Common Stock 149,744 ( 3 ) I By Teekell Investments, LP Common Stock 18,639 ( 4 ) I By White Knight Communications, LP

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 (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 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 (MM/DD/YY) 7. Title and Amount of Underlying Securities (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 of Derivative Security: 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 Series B Preferred Stock ( 5 ) ( 5 ) ( 5 ) Common Stock 30,000 D Nonvoting Common Stock ( 6 ) ( 6 ) ( 6 ) Common Stock 31,242 D Series B Preferred Stock ( 5 ) ( 5 ) ( 5 ) Common Stock 30,000 ( 7 ) I By estate of Byrum W. Teekell Nonvoting Common Stock ( 6 ) ( 6 ) ( 6 ) Common Stock 138,131 ( 8 ) I By estate of Byrum W. Teekell Stock Option (Right to Buy) $ 12 ( 9 ) 06/19/2026 Nonvoting Common Stock 22,667 D Stock Option (Right to Buy) $ 12 ( 9 ) 05/31/2027 Nonvoting Common Stock 13,500 D Stock Option (Right to Buy) $ 12 ( 9 ) 04/30/2028 Nonvoting Common Stock 12,833 D Stock Option (Right to Buy) $ 12 ( 9 ) 05/31/2029 Nonvoting Common Stock 12,500 D Stock Option (Right to Buy) $ 12 ( 9 ) 06/30/2029 Nonvoting Common Stock 5,000 D Stock Option (Right to Buy) $ 14 ( 9 ) 06/30/2030 Nonvoting Common Stock 28,125 D Stock Option (Right to Buy) $ 16.14 ( 9 ) 05/31/2031 Nonvoting Common Stock 20,556 D Stock Option (Right to Buy) $ 25.98 ( 10 ) 06/30/2032 Common Stock 9,247 D Stock Option (Right to Buy) $ 19.84 ( 10 ) 03/26/2033 Common Stock 5,783 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Teekell Judson Gray C/O MIAMI INTERNATIONAL HOLDINGS, INC. 7 ROSZEL ROAD, SUITE 1A PRINCETON, NJ08540 X Signatures /s/Alessandra Maria Corona Henriques, Attorney-in-Fact 08/13/2025 Signature of Reporting Person Date

Explanation of Responses:

( 1 )18,414 shares of common stock held in the estate of Byrum W. Teekell for which J. Gray Teekell is executor and disclaims beneficial ownership as to 13,811 shares of common stock. The inclusion of such 13,811 shares in this report shall not be deemed an admission of beneficial ownership of the reported shares for purposes of Section 16 or for any other purpose. ( 2 )57,219 shares of common stock held by Teekell Oil & Gas, Inc. as to which J. Gray Teekell is the president and a stockholder and disclaims beneficial ownership as to 42,914 of such shares. The inclusion of such 42,914 shares in this report shall not be deemed an admission of beneficial ownership of the reported shares for purposes of Section 16 or for any other purpose. ( 3 )149,744 shares of common stock held by Teekell Investments, LP as to which J. Gray Teekell is a limited partner and successor trustee of the trust that serves as its general partner and he disclaims beneficial ownership as to 112,308 of such shares. The inclusion of such 112,308 shares in this report shall not be deemed an admission of beneficial ownership of the reported shares for purposes of Section 16 or for any other purpose. ( 4 )18,639 shares of common stock, held by White Knight Communications, LP in which J. Gray Teekell is a limited partner and successor trustee of the trust that serves as its general partner and he disclaims beneficial ownership as to 16,309 of such shares. The inclusion of such 16,309 shares in this report shall not be deemed an admission of beneficial ownership of the reported shares for purposes of Section 16 or for any other purpose. ( 5 )The shares of Series B Preferred Stock are convertible on a one-for-one basis into shares of common stock commencing at the time of the Company's initial public offering ("IPO") effective date, which is August 13, 2025. The Series B Preferred Stock has no expiration date. ( 6 )The shares of nonvoting common stock are convertible on a one-for-one basis into shares of common stock commencing at any time. The nonvoting common stock has no expiration date. ( 7 )30,000 shares of Series B preferred stock, held in the estate of Byrum W. Teekell for which J. Gray Teekell is executor and disclaims beneficial ownership as to 22,500 shares of Series B preferred stock. The inclusion of such 22,500 shares in this report shall not be deemed an admission of beneficial ownership of the reported shares for purposes of Section 16 or for any other purpose. ( 8 )38,132 shares of nonvoting common stock held in the estate of Byrum W. Teekell for which J. Gray Teekell is executor and disclaims beneficial ownership as to 28,599 shares of nonvoting common stock. The inclusion of such 28,599 shares in this report shall not be deemed an admission of beneficial ownership of the reported shares for purposes of Section 16 or for any other purpose. ( 9 )The options are fully vested. The options were granted initially as the right to buy nonvoting common stock. On the closing date of the IPO, these will convert to the right to buy common stock instead of nonvoting common stock. ( 10 )The options are fully vested.

Remarks: See Exhibit 24.1 - Power of Attorney

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

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