Miami International CEO sells 54,229 shares

Miami International Holdings Chairman & CEO Thomas P. Gallagher, through Gallagher Investments, LLC, executed an exercise-and-sell transaction in MIAX common stock.

Rhea-AI Filing Summary

Miami International Holdings Chairman & CEO Thomas P. Gallagher, through Gallagher Investments, LLC, executed an exercise-and-sell transaction in MIAX common stock. On May 4, 2026, Gallagher Investments exercised 54,229 nonqualified stock options at $12.00 per share and sold 54,229 common shares in open-market trades at an average price of $47.26 per share.

All transactions were made under a previously established Rule 10b5-1 Plan adopted on December 29, 2025. After these transactions, Gallagher Investments held 1,723,275 MIAX common shares indirectly for Mr. Gallagher and retained 225,771 nonqualified stock options that are fully vested and remain exercisable until August 2, 2026.

Insider Trade Summary 10b5-1

Exercise and Sale: 54,229 shares ($1.91M approx. pre-tax spread)

Exercise and Sale 3 txns

Insider Gallagher Thomas P.

Role Chairman & CEO

Sold 54,229 shs ($2.56M)

Approx. gross sale proceeds $2.56M

Approx. exercise cost $651K

Approx. pre-tax spread $1.91M

Type	Security	Shares	Price	Value
Exercise	Nonqualified Stock Option (Right to Buy)	54,229	$0.00	$0.00
Exercise	Common Stock	54,229	$12.00	$651K
Sale	Common Stock	54,229	$47.26	$2.56M

Holdings After Transaction: Nonqualified Stock Option (Right to Buy) — 225,771 contracts (Indirect, By Gallagher Investments, LLC); Common Stock — 1,723,275 shares (Indirect, By Gallagher Investments, LLC)

Footnotes (3)

1. F1. This transaction was effected pursuant to a previously established Rule 10b5-1 Plan adopted by the Reporting Person on December 29, 2025.
2. F2. Mr. Gallagher maintains beneficial ownership, including dispositive and voting control, over Gallagher Investments, LLC.
3. F3. The options are fully vested.

Key Figures

Shares sold: 54,229 shares Sale price: $47.26 per share Options exercised: 54,229 options +5 more

8 metrics

Shares sold 54,229 shares Open-market sale of MIAX common stock on May 4, 2026

Sale price $47.26 per share Average price for 54,229 MIAX shares sold

Options exercised 54,229 options Nonqualified stock options exercised at $12.00 per share

Exercise price $12.00 per share Strike price of exercised nonqualified stock options

Shares held after 1,723,275 shares MIAX common stock indirectly held after transactions

Options remaining 225,771 options Nonqualified stock options remaining after exercise, fully vested

Option expiration August 2, 2026 Expiration date of remaining nonqualified stock options

Rule 10b5-1 plan date December 29, 2025 Adoption date of pre-arranged trading plan

Key Terms

Rule 10b5-1 Plan, Nonqualified Stock Option, beneficial ownership, dispositive and voting control

4 terms

Rule 10b5-1 Plan regulatory

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

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

"Nonqualified Stock Option (Right to Buy)"

A nonqualified stock option (NQSO) is a company grant that gives an individual the right to buy shares at a set price but does not meet special tax rules for incentive stock options; when exercised the difference between the market price and the exercise price is treated as ordinary income for the recipient and as a tax-deductible expense for the company. It matters to investors because NQSOs affect an employee’s after-tax proceeds, the company’s reported expenses, and potential share dilution—think of it like a cash bonus that converts into stock but is taxed as regular pay when you take it.

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

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

FAQ

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

What insider transaction did MIAX Chairman & CEO Thomas P. Gallagher report?

Thomas P. Gallagher reported an exercise-and-sell transaction involving 54,229 MIAX common shares. Gallagher Investments, LLC exercised 54,229 nonqualified stock options and sold the same number of shares in open-market trades on May 4, 2026 under a pre-established trading plan.

How many MIAX shares did Gallagher’s entity sell and at what price?

Gallagher Investments, LLC sold 54,229 MIAX common shares at an average price of $47.26 per share. These were open-market sales executed on May 4, 2026, immediately following the exercise of corresponding nonqualified stock options.

What stock options did Gallagher exercise in this MIAX Form 4 filing?

Gallagher Investments, LLC exercised 54,229 nonqualified stock options to buy MIAX common stock at a $12.00 exercise price. The options were fully vested and converted into common shares before those shares were sold in the open market on May 4, 2026.

How many MIAX shares does Gallagher’s entity hold after the reported transactions?

Following the May 4, 2026 transactions, Gallagher Investments, LLC held 1,723,275 MIAX common shares indirectly for Thomas P. Gallagher. This figure reflects the position after exercising 54,229 options and selling 54,229 common shares in open-market transactions.

Were the MIAX insider sales by Gallagher pre-planned under Rule 10b5-1?

Yes. The filing states the transactions were effected under a previously established Rule 10b5-1 Plan adopted by Thomas P. Gallagher on December 29, 2025. Such plans pre-schedule trades, making the timing less discretionary for the insider.

What MIAX stock options remain for Gallagher’s entity after this Form 4?

After exercising 54,229 nonqualified stock options, Gallagher Investments, LLC still holds 225,771 nonqualified stock options linked to MIAX common stock. The filing notes these options are fully vested and carry an expiration date of August 2, 2026.

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

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Accepted by SEC EDGAR 05/05/2026 - 08:17 AM 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)
05/04/2026

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)
			Code	V	Amount	(A) or (D)	Price
Common Stock	05/04/2026		M(1)		54,229	A	$12	1,777,504	I	By Gallagher Investments, LLC(2)
Common Stock	05/04/2026		S(1)		54,229	D	$47.26	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)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Nonqualified Stock Option (Right to Buy)	$12	05/04/2026		M(1)			54,229	(3)	08/02/2026	Common Stock	54,229	$0	225,771	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. The options are fully vested.

Remarks:

	/s/Alessandra Maria Corona Henriques, Attorney-in-Fact	05/05/2026
	** 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)