IMSR officer reports 134,109 stock options at $9.1717 on Form 3

Rhea-AI Filing Summary

Terrestrial Energy Inc. reported initial beneficial ownership for an officer on Form 3. The filing lists a stock option to purchase 134,109 shares of common stock at $9.1717 per share, exercisable on 07/09/2026 and expiring on 07/09/2045.

The option was granted under the company’s Second Amended and Restated 2024 Stock Option Plan and vests in one‑third increments on each of the first, second, and third anniversaries of the grant date, contingent on continued service.

Insider Trade Summary

1 transaction reported

Mixed 1 txn

Insider Millsap Steven M.

Role GC, Sec'y & Chief Comp. Off'r

Type	Security	Shares	Price	Value
holding	Stock Option (Right to Buy)	--	--	--

Holdings After Transaction: Stock Option (Right to Buy) — 134,109 shares (Direct)

Footnotes (1)

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Understanding Insider Trading Forms →

SEC Form 3

FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person^*

Millsap Steven M.

(Last) (First) (Middle)

2730 W. TYVOLA ROAD, SUITE 100

(Street)

CHARLOTTE NC 28217

(City) (State) (Zip)

2. Date of Event Requiring Statement (Month/Day/Year)
10/28/2025

3. Issuer Name and Ticker or Trading Symbol
Terrestrial Energy Inc. /DE/ [ IMSR ]

4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	GC, Sec'y & Chief Comp. Off'r

5. 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 Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Stock Option (Right to Buy)	07/09/2026(1)	07/09/2045	Common Stock	134,109	$9.1717	D

Explanation of Responses:

1. Consists of options granted pursuant to the Terrestrial Energy Inc. Second Amended and Restated 2024 Stock Option Plan. The options vest in one-third increments on each of the first, second and third anniversaries of the grant date, subject to the reporting person's continued service through each applicable vesting date.

Remarks:

Exhibit List - Exhibit 24.1 - Power of Attorney

	/s/ Steven M. Millsap	11/07/2025
	** 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 5 (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 did Terrestrial Energy (IMSR) disclose on Form 3?

An officer reported a stock option for 134,109 common shares at an exercise price of $9.1717 per share.

When do the reported options become exercisable?

They are first exercisable on 07/09/2026 and expire on 07/09/2045.

What is the vesting schedule for the 134,109-share option?

It vests in one‑third increments on the first, second, and third anniversaries of the grant date, subject to continued service.

Under which plan were the options granted?

The options were granted under the Second Amended and Restated 2024 Stock Option Plan.

What is the ownership form of the reported derivative security?

The ownership form is Direct (D).

Which officer filed the Form 3 and what roles do they hold?

The reporting person is an officer serving as GC, Secretary & Chief Compensation Officer.