MIAX CEO sells 149,700 shares at $41.13 average

MIAMI INTERNATIONAL HOLDINGS, INC.

Rhea-AI Filing Summary

MIAMI INTERNATIONAL HOLDINGS, INC. (MIAX) reported insider transactions by Chairman & CEO Thomas P. Gallagher, effected through Gallagher Investments, LLC. On August 19, 2026, the entity sold 149,700 shares of common stock at a weighted average price of $41.13 per share under a previously adopted Rule 10b5-1 Plan. On August 18, 2026, 150,300 shares were surrendered to the company to satisfy tax withholding obligations upon net settlement of restricted stock awards, which is disclosed as not representing a market sale. Gallagher is stated to maintain beneficial ownership, including voting and dispositive control, over Gallagher Investments, LLC.

Insider Trade Summary 10b5-1

Net Seller: 149,700 shares

Net Sell 2 txns

Insider Gallagher Thomas P.

Role Chairman & CEO

Sold 149,700 shs ($6.16M)

Type	Security	Shares	Price	Value
Sale	Common Stock F3, F4, F2	149,700	$41.13	$6.16M
Tax Withholding	Common Stock F1, F2	150,300	$42.41	$6.37M

Holdings After Transaction: Common Stock — 1,423,275 shares (Indirect, By Gallagher Investments, LLC)

Footnotes (4)

1. F1. 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. F2. Mr. Gallagher maintains beneficial ownership, including dispositive and voting control, over Gallagher Investments, LLC.
3. F3. This transaction was effected pursuant to a previously established Rule 10b5-1 Plan adopted by the Reporting Person on December 29, 2025.
4. F4. This transaction was executed in multiple trades throughout the day at prices ranging from $38.85 to $42.56. The price reported above reflects the weighted average sales price. The Reporting Person hereby undertakes to provide upon request to the Securities and Exchange Commission staff, the Issuer or a security holder of the Issuer, full information regarding the number of shares and prices at which the transaction was effected.

Key Figures

Shares sold: 149,700 shares of Common Stock Weighted average sale price: $41.13 per share Shares surrendered for tax withholding: 150,300 shares of Common Stock +1 more

4 metrics

Shares sold 149,700 shares of Common Stock Open-market or private sale on August 19, 2026 under Rule 10b5-1 Plan

Weighted average sale price $41.13 per share 149,700-share sale on August 19, 2026; individual trades ranged from $38.85 to $42.56

Shares surrendered for tax withholding 150,300 shares of Common Stock Surrendered on August 18, 2026 to satisfy tax withholding for net settlement of restricted stock awards

Tax-related surrender reference price $42.41 per share Price associated with 150,300-share surrender for tax withholding on August 18, 2026

Key Terms

Rule 10b5-1 Plan, net settlement, beneficial ownership, dispositive and voting control, +1 more

5 terms

Rule 10b5-1 Plan regulatory

"This transaction was effected pursuant to a previously established Rule 10b5-1 Plan"

A Rule 10b5-1 plan is a prearranged, written schedule that lets corporate insiders buy or sell company stock at set times or amounts, even if they later learn material nonpublic information. Think of it like setting an automatic thermostat for trades: it creates a clear record that trades were planned in advance, reducing the risk of insider-trading accusations and helping investors trust that insider transactions are routine rather than based on secret information.

net settlement financial

"in connection with the net settlement of restricted stock awards"

beneficial ownership financial

"Mr. Gallagher maintains beneficial ownership, including dispositive and voting control"

Beneficial ownership means the person or entity that actually enjoys the benefits of owning shares or other assets — such as receiving dividends, voting rights, or price gains — even if the legal title is held in another name. For investors it matters because knowing who truly controls and profits from a company reveals who can influence decisions, exposes potential conflicts of interest or hidden concentration of power, and affects transparency and risk in the stock.

dispositive and voting control financial

"beneficial ownership, including dispositive and voting control, over Gallagher Investments, LLC"

tax withholding and remittance obligations financial

"to satisfy tax withholding and remittance obligations in connection with the net settlement"

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What insider transactions did MIAX report for Thomas P. Gallagher in this Form 4?

The filing reports a sale of 149,700 MIAX shares on August 19, 2026 at a weighted average price of $41.13, and a surrender of 150,300 shares on August 18, 2026 to cover tax withholding from restricted stock awards.

Was the MIAX insider sale by Thomas P. Gallagher made under a Rule 10b5-1 plan?

Yes. The sale of 149,700 MIAX shares on August 19, 2026 was effected pursuant to a previously established Rule 10b5-1 Plan adopted by the reporting person on December 29, 2025.

Does the 150,300-share MIAX transaction represent a sale by Thomas P. Gallagher?

No. The 150,300 shares on August 18, 2026 were surrendered to the company to satisfy tax withholding and remittance obligations from net settlement of restricted stock awards and are explicitly stated not to represent a sale.

Through what entity were Thomas P. Gallagher’s MIAX transactions made?

Both transactions involve indirect ownership by Gallagher Investments, LLC. The filing states that Thomas P. Gallagher maintains beneficial ownership, including voting and dispositive control, over Gallagher Investments, LLC.

What price information is provided for the MIAX insider sale on August 19, 2026?

The 149,700 MIAX shares sold on August 19, 2026 were executed in multiple trades at prices ranging from $38.85 to $42.56. The reported price of $41.13 is the weighted average sales price for those trades.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Available on EDGAR 08/20/2026 - 04:12 PM EDT Accepted by SEC EDGAR 08/20/2026 - 04:12 PM EDT Learn about SEC filing dates

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
Estimated average burden
hours per response:			0.5

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

X

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 NEW JERSEY 08540

(City) (State) (Zip)

UNITED STATES

(Country)

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

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
08/18/2026

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

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

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

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	08/18/2026		F		150,300(1)	D	$42.41	1,572,975	I	By Gallagher Investments, LLC(2)
Common Stock	08/19/2026		S(3)		149,700	D	$41.13(4)	1,423,275	I	By Gallagher Investments, LLC(2)

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. This transaction was effected pursuant to a previously established Rule 10b5-1 Plan adopted by the Reporting Person on December 29, 2025.

4. This transaction was executed in multiple trades throughout the day at prices ranging from $38.85 to $42.56. The price reported above reflects the weighted average sales price. The Reporting Person hereby undertakes to provide upon request to the Securities and Exchange Commission staff, the Issuer or a security holder of the Issuer, full information regarding the number of shares and prices at which the transaction was effected.

Remarks:

	/s/Alessandra Maria Corona Henriques, Attorney-in-Fact	08/20/2026
	** 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.
* Form 4: SEC 1474 (03-26)