[Form 4] Miami International Holdings, Inc. Insider Trading Activity

Rhea-AI Filing Summary

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.

Positive

• Insider clarified that the 192,220-share disposition was a tax withholding surrender and not an open-market sale
• Substantial remaining ownership of 1,848,274 shares indirectly via Gallagher Investments, LLC
• Correction filed to reflect an additional 2,000-share purchase, improving reporting accuracy

Negative

• Large number of shares surrendered (192,220) reduced the reporting person’s direct economic interest, even if for tax purposes

Insights

Securities Analyst

TL;DR Insider surrendered shares to cover taxes on restricted stock; not an open-market sale and overall holdings remain substantial.

The reported disposition of 192,220 shares is identified as a surrender to satisfy tax withholding from net-settled restricted stock awards, which the filer explicitly states is not a sale. That distinction matters because open-market selling can signal liquidity-driven insider exit while tax withholding does not necessarily indicate reduced confidence. Post-transaction indirect beneficial ownership of 1,848,274 shares via Gallagher Investments, LLC remains sizable relative to typical insider stakes. The corrected addition of 2,000 shares on 08/13/2025 is immaterial in scale but shows an update to previously reported holdings. Overall, this filing is routine and neutral for investors absent other context.

Corporate Governance Expert

TL;DR Transaction appears procedural for tax settlement; disclosure correction improves record accuracy but raises no governance red flags.

The Form 4 clarifies the nature of the disposition as tax-related surrender linked to restricted stock net settlement and not an open-market disposal, which reduces concerns about opportunistic insider selling. Maintaining beneficial ownership through Gallagher Investments, LLC and the explicit statement of voting/dispositive control over that vehicle are appropriate disclosures. The amendment to correct prior holdings demonstrates attention to filing accuracy. There are no indicated changes to officer status or control that would suggest governance issues from this filing alone.

SEC Form 4

FORM 4

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
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
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Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Gallagher Thomas P.

(Last) (First) (Middle)

C/O MIAMI INTERNATIONAL HOLDINGS, INC

7 ROSZEL ROAD, SUITE 1A

(Street)

PRINCETON NJ 08540

(City) (State) (Zip)

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
X	Officer (give title below)		Other (specify below)
	Chairman & CEO

3. Date of Earliest Transaction (Month/Day/Year)
08/26/2025

4. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	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	08/26/2025		F		192,220(1)	D	$33.9	1,848,274	I	By Gallagher Investments, LLC(2)
Common Stock								587,963(3)	D

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 (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	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 (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (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: 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

Explanation of Responses:

1. Represents shares that have been surrendered to the Company to satisfy tax withholding and remittance obligations in connection with the net settlement of restricted stock awards and does not represent a sale by the reporting person.

2. Mr. Gallagher maintains beneficial ownership, including dispositive and voting control, over Gallagher Investments, LLC.

3. Corrects previously reported holdings to reflect an additional 2,000 shares purchased on August 13, 2025, which are held jointly with his spouse with right of survival.

Remarks:

	/s/Alessandra Maria Corona Henriques, Attorney-in-Fact	08/28/2025
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.

FAQ

What did Thomas P. Gallagher report on the Form 4 for MIAX?

He reported a disposition of 192,220 shares on 08/26/2025 surrendered to satisfy tax withholding from net-settled restricted stock awards and corrected prior holdings to add 2,000 shares purchased on 08/13/2025.

Was the 192,220-share disposition an open-market sale?

No. The filing explicitly states the shares were surrendered to satisfy tax withholding and "does not represent a sale by the reporting person."

How many MIAX shares does Gallagher beneficially own after the transaction?

1,848,274 shares are reported as beneficially owned indirectly through Gallagher Investments, LLC following the transaction.

Why was a correction made in this Form 4?

The correction reflects an additional 2,000 shares purchased on 08/13/2025 that are held jointly with his spouse with right of survival.

Who signed the Form 4 and when?

An attorney-in-fact, Alessandra Maria Corona Henriques, signed the form on 08/28/2025.

Does Gallagher still control the shares held by Gallagher Investments, LLC?

Yes. The filing states Mr. Gallagher maintains beneficial ownership, including dispositive and voting control, over Gallagher Investments, LLC.