How are Thomas P. Gallagher’s MIAX-related derivative holdings affected by this transaction?

After exercising 48,334 options, Gallagher, through Gallagher Investments, LLC, indirectly held 235,000 derivative securities . These represent remaining nonqualified stock options in Miami International, as reported following the 2026-08-04 exercise and sale of MIAX common shares.

Miami International Holdings (NYSE: MIAX) CEO reports 48,334-share sale

Q: What insider transactions did MIAX Chairman Thomas P. Gallagher report?

Thomas P. Gallagher reported exercising 48,334 options and acquiring 48,334 Miami International common shares, then selling 48,334 shares on 2026-08-04. All trades were executed indirectly through Gallagher Investments, LLC under a pre-established Rule 10b5-1 trading plan.

Q: How many MIAX shares did Thomas P. Gallagher exercise and sell on 2026-08-04?

On 2026-08-04, Thomas P. Gallagher exercised options for 48,334 shares of Miami International common stock and sold 48,334 shares . The exercise involved nonqualified stock options indirectly held via Gallagher Investments, LLC, with all transactions disclosed for MIAX investors.

Q: At what prices were Thomas P. Gallagher’s MIAX trades executed?

Gallagher’s option exercise used a $12.00 per-share price, and the subsequent share sale had a $45.69 weighted average price. Sale trades were executed in a price range from $45.09 to $46.78 , as reported for the MIAX common stock transactions.

Q: Were the MIAX insider trades made under a Rule 10b5-1 plan?

Yes. All reported transactions were effected under a Rule 10b5-1 Plan adopted on December 29, 2025 . This pre-arranged trading plan governs the timing and amount of Gallagher’s MIAX option exercises and related stock sales through Gallagher Investments, LLC.

Q: How is ownership of the MIAX shares structured for these transactions?

The options and common shares are held indirectly through Gallagher Investments, LLC , over which Thomas P. Gallagher maintains beneficial ownership including voting and dispositive control. The Form 4 attributes these MIAX transactions to him via this controlled entity.

Filing Impact

(Neutral)

Filing Sentiment

(Neutral)

Form Type

Rhea-AI Filing Summary

Miami International Holdings, Inc. reported insider transactions by Chairman & CEO Thomas P. Gallagher on 2026-08-04. Through Gallagher Investments, LLC, he exercised 48,334 nonqualified stock options at $12.00 per share, acquired 48,334 common shares, and sold the same amount at a weighted average of $45.69 per share in trades ranging from $45.09 to $46.78. The options were fully vested, 235,000 derivative securities remained indirectly held after the exercise, and all trades occurred under a Rule 10b5-1 plan adopted on December 29, 2025.

Insider Trade Summary 10b5-1

Exercise and Sale: 48,334 shares ($1.63M approx. pre-tax spread)

Exercise and Sale 3 txns

Insider Gallagher Thomas P.

Role Chairman & CEO

Sold 48,334 shs ($2.21M)

Approx. gross sale proceeds $2.21M

Approx. exercise cost $580K

Approx. pre-tax spread $1.63M

Type	Security	Shares	Price	Value
Exercise	Nonqualified Stock Option (Right to Buy) ^{F1, F4, F2}	48,334	$0.00	$0.00
Exercise	Common Stock ^{F1, F2}	48,334	$12.00	$580K
Sale	Common Stock ^{F1, F3, F2}	48,334	$45.69	$2.21M

Holdings After Transaction: Nonqualified Stock Option (Right to Buy) — 235,000 shares (Indirect, By Gallagher Investments, LLC); Common Stock — 1,723,275 shares (Indirect, By Gallagher Investments, LLC)

Footnotes (4)

F1. This transaction was effected pursuant to a previously established Rule 10b5-1 Plan adopted by the Reporting Person on December 29, 2025.
F2. Mr. Gallagher maintains beneficial ownership, including dispositive and voting control, over Gallagher Investments, LLC.
F3. This transaction was executed in multiple trades throughout the day at prices ranging from $45.09 to $46.78. 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.
F4. The options are fully vested.

Key Figures

Options exercised: 48,334 shares Exercise price: $12.00 per share Shares sold: 48,334 shares +3 more

6 metrics

Options exercised 48,334 shares Nonqualified stock options exercised on 2026-08-04

Exercise price $12.00 per share Conversion or exercise price of nonqualified stock options

Shares sold 48,334 shares Common stock sold indirectly via Gallagher Investments, LLC on 2026-08-04

Weighted average sale price $45.69 per share Common stock sale; individual trades ranged from $45.09 to $46.78

Sale price range $45.09–$46.78 per share Price range for multiple trades comprising the reported sale

Remaining derivative securities 235,000 shares Nonqualified stock options indirectly owned after the option exercise

Key Terms

Rule 10b5-1 Plan, Nonqualified Stock Option, weighted average sales price, beneficial ownership

4 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.

Nonqualified Stock Option financial

"security_title: Nonqualified Stock Option (Right to Buy)"

weighted average sales price financial

"price reported above reflects the weighted average sales price"

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.

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

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Form 4 Insider Transactions: What Each Field Means →

Available on EDGAR 08/06/2026 - 04:08 PM Accepted by SEC EDGAR 08/06/2026 - 04:05 PM

FAQ

What insider transactions did MIAX Chairman Thomas P. Gallagher report?

Thomas P. Gallagher reported exercising 48,334 options and acquiring 48,334 Miami International common shares, then selling 48,334 shares on 2026-08-04. All trades were executed indirectly through Gallagher Investments, LLC under a pre-established Rule 10b5-1 trading plan.

How many MIAX shares did Thomas P. Gallagher exercise and sell on 2026-08-04?

On 2026-08-04, Thomas P. Gallagher exercised options for 48,334 shares of Miami International common stock and sold 48,334 shares. The exercise involved nonqualified stock options indirectly held via Gallagher Investments, LLC, with all transactions disclosed for MIAX investors.

At what prices were Thomas P. Gallagher’s MIAX trades executed?

Gallagher’s option exercise used a $12.00 per-share price, and the subsequent share sale had a $45.69 weighted average price. Sale trades were executed in a price range from $45.09 to $46.78, as reported for the MIAX common stock transactions.

Were the MIAX insider trades made under a Rule 10b5-1 plan?

Yes. All reported transactions were effected under a Rule 10b5-1 Plan adopted on December 29, 2025. This pre-arranged trading plan governs the timing and amount of Gallagher’s MIAX option exercises and related stock sales through Gallagher Investments, LLC.

How is ownership of the MIAX shares structured for these transactions?

The options and common shares are held indirectly through Gallagher Investments, LLC, over which Thomas P. Gallagher maintains beneficial ownership including voting and dispositive control. The Form 4 attributes these MIAX transactions to him via this controlled entity.

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).

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)
08/04/2026

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)
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	Code	V	Amount	(A) or (D)	Price		6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
Common Stock	08/04/2026		M⁽¹⁾		48,334	A	$12	1,771,609	I	By Gallagher Investments, LLC⁽²⁾
Common Stock	08/04/2026		S⁽¹⁾		48,334	D	$45.69⁽³⁾	1,723,275	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)
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)	Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares	8. Price of Derivative Security (Instr. 5)		10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
Nonqualified Stock Option (Right to Buy)	$12	08/04/2026		M⁽¹⁾			48,334	⁽⁴⁾	05/28/2028	Common Stock	48,334	$0	235,000	I	By Gallagher Investments, LLC⁽²⁾

Explanation of Responses:

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

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

3. This transaction was executed in multiple trades throughout the day at prices ranging from $45.09 to $46.78. 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.

4. The options are fully vested.

Remarks:

	/s/Alessandra Maria Corona Henriques, Attorney-in-Fact	08/06/2026
	** 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)

Source: View Original Filing on SEC EDGAR