Gallagher to sell 141K MIAX shares under Rule 144

MIAMI INTERNATIONAL HOLDINGS, INC.

Rhea-AI Filing Summary

MIAMI INTERNATIONAL HOLDINGS, INC. (MIAX) is the issuer for a proposed Rule 144 sale by Gallagher Investments LLC. Gallagher Investments LLC has notified that it intends to sell 141,000 shares of common stock, to be received upon the exercise of stock options, with an aggregate market value of $5,727,420. The notice lists 99,230,898 shares outstanding of the same class as of September 3, 2026; this is a baseline figure, not the amount being sold. Prior 10b5‑1 plan sales by Gallagher Investments LLC over the past three months are also reported.

Key Figures

Shares to be sold under Rule 144: 141,000 shares Aggregate market value of planned sale: $5,727,420 Shares outstanding: 99,230,898 shares +5 more

8 metrics

Shares to be sold under Rule 144 141,000 shares Common stock to be sold for account of Gallagher Investments LLC

Aggregate market value of planned sale $5,727,420 Market value of 141,000 MIAX shares referenced in the notice

Shares outstanding 99,230,898 shares Common stock outstanding as of September 3, 2026

10b5-1 sale on August 19, 2026 149,700 shares for $6,157,894.53 Common stock sold by Gallagher Investments LLC under a 10b5‑1 plan

10b5-1 sale on August 4, 2026 48,334 shares for $2,208,288.63 Common stock sold by Gallagher Investments LLC under a 10b5‑1 plan

10b5-1 sale on July 13, 2026 70,000 shares for $2,976,698.67 Common stock sold by Gallagher Investments LLC under a 10b5‑1 plan

10b5-1 sale on July 7, 2026 28,228 shares for $1,193,200.38 Common stock sold by Gallagher Investments LLC under a 10b5‑1 plan

10b5-1 sale on July 6, 2026 41,772 shares for $1,758,292.77 Common stock sold by Gallagher Investments LLC under a 10b5‑1 plan

Key Terms

Rule 144, 10b5-1, Exercise of Stock Options, Form 144, +1 more

5 terms

Rule 144 regulatory

"See the definition of "person" in paragraph (a) of Rule 144."

Rule 144 is a U.S. securities regulation that sets conditions under which restricted or insider-held shares can be legally resold to the public, such as required holding periods, availability of public information, limits on how much can be sold at once, and certain filing requirements. For investors it matters because it determines when previously locked-up shares can enter the market — like a release valve that can increase supply, affect share price, and signal insider intent.

10b5-1 regulatory

"10b5-1 Sales for GALLAGHER INVESTMENTS LLC 7 Roszel Road, Suite 1A"

A 10b5-1 plan is a pre-set schedule that lets company insiders buy or sell shares according to written instructions made when they do not possess material, nonpublic information. Think of it as a timed automatic payment for stock trades: it helps insiders avoid accusations of trading on secret information and gives outside investors a clearer signal about whether sales are routine or potentially informative about the company’s prospects.

Exercise of Stock Options financial

"Common | 09/03/2026 | Exercise of Stock Options | Issuer"

Form 144 regulatory

"144: Filer Information"

Form 144 is a document that investors must file with the government when they plan to sell a large number of shares of a company's stock. It helps ensure transparency so everyone knows how many shares are being sold and when, which can impact the stock's price.

Aggregate market value financial

"Common | Morgan Stanley Smith Barney LLC Executive Financial Services"

Aggregate market value is the combined price you would pay to buy all outstanding shares of a company or all companies in a group at current market prices — essentially the sum of each stock’s market capitalization. It matters to investors because it shows the overall size and weight of an investment or sector (like the total cost to buy every piece of a puzzle), helps compare scale across companies or markets, and influences index composition and risk exposure.

FAQ

What does the Form 144 filing disclose for MIAX?

The filing discloses that Gallagher Investments LLC has given notice under Rule 144 of its intent to sell 141,000 shares of MIAMI INTERNATIONAL HOLDINGS, INC. common stock, to be obtained through the exercise of stock options and sold for cash through a broker.

How many MIAX shares does Gallagher Investments LLC plan to sell under this Form 144?

Gallagher Investments LLC plans to sell 141,000 shares of MIAMI INTERNATIONAL HOLDINGS, INC. common stock. The shares are to be received upon the exercise of stock options, with the sales expected to occur over the next three months as described in the notice.

What is the reported market value of the MIAX shares to be sold?

The reported aggregate market value of the 141,000 shares of MIAMI INTERNATIONAL HOLDINGS, INC. common stock to be sold is $5,727,420, as stated in the securities information section associated with the planned Rule 144 transaction.

How many MIAX shares were outstanding as referenced in the Form 144?

The notice states that there were 99,230,898 shares outstanding of MIAMI INTERNATIONAL HOLDINGS, INC. common stock as of September 3, 2026. This figure provides context for the size of the planned Rule 144 sale relative to the total outstanding shares.

What prior 10b5-1 sales by Gallagher Investments LLC in MIAX stock are reported?

Reported 10b5‑1 sales by Gallagher Investments LLC include 149,700 shares on August 19, 2026 for $6,157,894.53, 48,334 shares on August 4, 2026 for $2,208,288.63, and additional July 2026 sales of common stock with specified share and dollar amounts.

How will the MIAX shares be acquired and sold in this Form 144 notice?

The notice states that the MIAX shares were and will be received upon the exercise of stock options, with the dates of acquisition and payment being the dates of exercise/sale. The method of acquisition is listed as Exercise of Stock Options, and the sale is for cash.

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Available on EDGAR 09/03/2026 - 05:50 PM Accepted by SEC EDGAR 09/03/2026 - 04:41 PM Learn about SEC filing dates

Form 144 Filer Information	UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Form 144 NOTICE OF PROPOSED SALE OF SECURITIES PURSUANT TO RULE 144 UNDER THE SECURITIES ACT OF 1933
FORM 144

144: Filer Information

Filer CIK	0002080477
Filer CCC	XXXXXXXX
Is this a LIVE or TEST Filing?	LIVE TEST
Submission Contact Information
Name
Phone
E-Mail Address

144: Issuer Information

Name of Issuer	MIAMI INTERNATIONAL HOLDINGS INC
SEC File Number	001-42805
Address of Issuer	7 Roszel Road, Suite 1A Princeton NEW JERSEY 08540
Phone	6098977300
Name of Person for Whose Account the Securities are To Be Sold	GALLAGHER INVESTMENTS LLC
See the definition of "person" in paragraph (a) of Rule 144. Information is to be given not only as to the person for whose account the securities are to be sold but also as to all other persons included in that definition. In addition, information shall be given as to sales by all persons whose sales are required by paragraph (e) of Rule 144 to be aggregated with sales for the account of the person filing this notice.
Relationship to Issuer	Director
Relationship to Issuer	Officer

144: Securities Information

Title of the Class of Securities To Be Sold	Name and Address of the Broker	Number of Shares or Other Units To Be Sold	Aggregate Market Value	Number of Shares or Other Units Outstanding	Approximate Date of Sale	Name the Securities Exchange
Common	Morgan Stanley Smith Barney LLC Executive Financial Services 1 New York Plaza 8th Floor New York NY 10004	141000	5727420.00	99230898	09/03/2026	NYSE

Furnish the following information with respect to the acquisition of the securities to be sold and with respect to the payment of all or any part of the purchase price or other consideration therefor:

144: Securities To Be Sold

Title of the Class	Date you Acquired	Nature of Acquisition Transaction	Name of Person from Whom Acquired	Is this a Gift?	Date Donor Acquired	Amount of Securities Acquired	Date of Payment	Nature of Payment *
Common	09/03/2026	Exercise of Stock Options	Issuer			141000	09/03/2026	Cash

* If the securities were purchased and full payment therefor was not made in cash at the time of purchase, explain in the table or in a note thereto the nature of the consideration given. If the consideration consisted of any note or other obligation, or if payment was made in installments describe the arrangement and state when the note or other obligation was discharged in full or the last installment paid.

Furnish the following information as to all securities of the issuer sold during the past 3 months by the person for whose account the securities are to be sold.

144: Securities Sold During The Past 3 Months

Name and Address of Seller	Title of Securities Sold	Date of Sale	Amount of Securities Sold	Gross Proceeds
10b5-1 Sales for GALLAGHER INVESTMENTS LLC 7 Roszel Road, Suite 1A Princeton NJ 08540	Common	08/19/2026	149700	6157894.53
10b5-1 Sales for GALLAGHER INVESTMENTS LLC 7 Roszel Road, Suite 1A Princeton NJ 08540	Common	08/04/2026	48334	2208288.63
10b5-1 Sales for GALLAGHER INVESTMENTS LLC 7 Roszel Road, Suite 1A Princeton NJ 08540	Common	07/13/2026	70000	2976698.67
10b5-1 Sales for GALLAGHER INVESTMENTS LLC 7 Roszel Road, Suite 1A Princeton NJ 08540	Common	07/07/2026	28228	1193200.38
10b5-1 Sales for GALLAGHER INVESTMENTS LLC 7 Roszel Road, Suite 1A Princeton NJ 08540	Common	07/06/2026	41772	1758292.77

144: Remarks and Signature

Remarks	The securities to be sold were and will be received upon the exercise of stock options over the next three months. The dates of acquisition and payment were and will be the dates of exercise/sale.
Date of Notice	09/03/2026
Date of Plan Adoption or Giving of Instruction, If Relying on Rule 10b5-1	12/29/2025
ATTENTION:
The person for whose account the securities to which this notice relates are to be sold hereby represents by signing this notice that he does not know any material adverse information in regard to the current and prospective operations of the Issuer of the securities to be sold which has not been publicly disclosed. If such person has adopted a written trading plan or given trading instructions to satisfy Rule 10b5-1 under the Exchange Act, by signing the form and indicating the date that the plan was adopted or the instruction given, that person makes such representation as of the plan adoption or instruction date.
Signature	/s/ Thomas P. Gallagher
ATTENTION: Intentional misstatements or omission of facts constitute Federal Criminal Violations (See 18 U.S.C. 1001)