[Form 4] MIAMI INTERNATIONAL HOLDINGS, INC. Insider Trading Activity

Rhea-AI Filing Summary

John Smollen, EVP Traded Products & Relation of Miami International Holdings, Inc. (MIAX), reported option exercises on 09/11/2025 and subsequent net settlement for tax withholding. The filing shows two nonqualified stock option exercises of 125,001 and 24,999 shares at an exercise price of $12 per share, and the surrender of 52,054 shares to satisfy tax-withholding obligations at an indicated price of $37.39 per share. The options were fully vested and exercisable on 09/17/2025. Following the transactions the reporting person beneficially owned 166,119 shares directly. The form is signed by an attorney-in-fact on 09/15/2025.

Positive

• Options fully vested before exercise, enabling the reporting person to exercise without vesting contingencies
• Post-transaction ownership disclosed with a clear direct beneficial ownership figure of 166,119 shares
• Net settlement for tax withholding was used rather than an open-market sale, indicating withholding compliance rather than cash liquidation

Negative

• 52,054 shares surrendered to satisfy tax-withholding obligations, which reduced the reporting person's direct holdings
• No sale to third parties is reported, so liquidity realized by the reporting person is not disclosed beyond tax withholding

Insights

Financial Analyst

TL;DR: Insider exercised vested options, increasing direct ownership while using shares to cover tax withholding; net position reported as 166,119 shares.

The reporting shows material option exercises executed at a $12 strike with net settlement for taxes of 52,054 shares reported as a disposition. The transactions do not state any sales to third parties; rather, surrendered shares were used solely to satisfy withholding. The disclosure confirms full vesting of the options and provides explicit post-transaction ownership counts, which are useful for assessing insider alignment with shareholders but do not indicate external monetization.

Corporate Governance Expert

TL;DR: Executive exercised fully vested options and followed standard net-settlement tax procedures; disclosure appears complete and timely.

The Form 4 documents option exercises and tax withholding via share surrender, which is a common practice that preserves immediate compliance with tax obligations. The filing includes transaction codes, amounts, exercise price, vesting confirmation, and a signature by an attorney-in-fact, meeting typical disclosure expectations. No indications of atypical related-party transactions or undisclosed derivative arrangements are present in the filing.

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

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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^*

Smollen John

(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)

	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	EVP Traded Products & Relation

3. Date of Earliest Transaction (Month/Day/Year)
09/11/2025

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	09/11/2025		M		125,001	A	$12	193,174	D
Common Stock	09/11/2025		F		52,054(1)	D	$37.39	141,120	D
Common Stock	09/11/2025		M		24,999	A	$12	166,119	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
Nonqualified Stock Option (Right to Buy)	$12	09/11/2025		M			125,001	(2)	09/17/2025	Common Stock	125,001	$0	0	D
Incentive Stock Option (Right to Buy)	$12	09/11/2025		M			24,999	(2)	09/17/2025	Common Stock	24,999	$0	0	D

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 options exercised and does not represent a sale by the reporting person.

2. The options are fully vested.

Remarks:

	/s/Alessandra Maria Corona Henriques, Attorney-in-Fact	09/15/2025
	** 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 transactions did MIAX insider John Smollen report on Form 4?

The Form 4 reports exercises of 125,001 and 24,999 stock options at an exercise price of $12 each on 09/11/2025, plus the surrender of 52,054 shares to cover tax withholding.

How many MIAX shares does John Smollen beneficially own after the transactions?

Following the reported transactions the filing shows Mr. Smollen beneficially owned 166,119 shares directly.

Were the options exercised by the MIAX reporting person vested?

Yes, the filing states the options are fully vested and exercisable as of the dates reported.

Did the Form 4 report any open-market sales of MIAX shares?

No. The only dispositions reported are the surrender of 52,054 shares to satisfy tax-withholding obligations; no sales to third parties are indicated.

When was the Form 4 signed and filed for the MIAX transactions?

The signature on the form is dated 09/15/2025, and the transactions are dated 09/11/2025.