IMSR Form 3: CFO discloses 156,461 stock options

Rhea-AI Filing Summary

Terrestrial Energy Inc. (IMSR) reported an initial insider ownership filing by its Chief Financial Officer. The Form 3 lists a stock option (right to buy) covering 156,461 shares of common stock at an exercise price of $7.8295. The option becomes exercisable on 04/30/2026 and expires on 04/30/2045. According to the company’s Second Amended and Restated 2024 Stock Option Plan, the award vests in one‑third increments on each of the first, second, and third anniversaries of the grant date, contingent on continued service.

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^*

Thrasher Brian Patrick

(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)
	Chief Financial Officer

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)	04/30/2026(1)	04/30/2045	Common Stock	156,461	$7.8295	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, pursuant to Power of Attorney	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).
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FAQ

What did Terrestrial Energy (IMSR) disclose in this Form 3?

The CFO reported a stock option to purchase 156,461 common shares at an exercise price of $7.8295.

When do the reported options for IMSR become exercisable and when do they expire?

They become exercisable on 04/30/2026 and expire on 04/30/2045.

What is the vesting schedule for the IMSR stock options?

They vest one‑third each on the first, second, and third anniversaries of the grant date, subject to continued service.

Who is the reporting person in this insider filing?

The reporting person is the company’s Chief Financial Officer.

Is the ownership of the derivative security direct or indirect?

The filing indicates Direct (D) ownership of the options.

What plan governs these IMSR stock options?

They were granted under the Terrestrial Energy Inc. Second Amended and Restated 2024 Stock Option Plan.

What is the date of the reportable event for this filing?

The event date is 10/28/2025.