Terrestrial Energy CEO acquires 55,432 shares

Q: How many IMSR shares did CEO Simon Irish receive from his RSUs?

On October 28, 2026, Simon Irish exercised/converted 55,432 restricted stock units, corresponding to the acquisition of 55,432 common shares.

Q: How do Simon Irish’s IMSR RSUs vest?

The restricted stock units vest pro rata over three years following the grant date, subject to continued employment through each applicable vesting date, with accelerated vesting in certain events.

The RSUs vest pro rata over three years following the grant date, subject to continued employment, with accelerated vesting in certain events.

Available on EDGAR 10/30/2026 - 09:18 AM EDT Accepted by SEC EDGAR 10/30/2026 - 09:17 AM EDT

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Rhea-AI Filing Summary

Terrestrial Energy Inc. (IMSR) Chief Executive Officer Simon Irish reported the exercise/conversion of 55,432 restricted stock units on October 28, 2026, corresponding to the acquisition of 55,432 common shares. Afterward, his reported direct holdings included 2,879,846 common shares and 110,866 restricted stock units; indirect common-share holdings were 2,818,520 through an LLC and 52,255 through an IRA.

Insider Trade Summary

55,432 shares exercised/converted

Exercise 2 txns

Insider Irish Simon

Role Chief Executive Officer

Type	Security	Shares	Price	Value
Exercise	Restricted Stock Units ^{F2, F3}	55,432	$0.00	$0.00
Exercise	Common Stock ^F1	55,432	$0.00	$0.00
Holding	Common Stock	--	--	--
Holding	Common Stock	--	--	--

Holdings After Transaction: Restricted Stock Units — 110,866 contracts (Direct); Common Stock — 2,879,846 shares (Direct); Common Stock — 2,818,520 shares (Indirect, Through LLC); Common Stock — 52,255 shares (Indirect, Through IRA)

Footnotes (3)

F1. Represents shares of common stock subject to vested portion of restricted stock unit award.
F2. Each restricted stock unit represents a contingent right to receive one share of common stock.
F3. The restricted stock units vest pro rata over a three year period following the grant date, subject to Mr. Irish's continued employment through each applicable vesting date and accelerated vesting in certain events.

Key Figures

Restricted stock units exercised/converted: 55,432 restricted stock units Common shares acquired: 55,432 shares Direct common shares following transaction: 2,879,846 shares +3 more

6 metrics

Restricted stock units exercised/converted 55,432 restricted stock units October 28, 2026

Common shares acquired 55,432 shares October 28, 2026

Direct common shares following transaction 2,879,846 shares Simon Irish’s reported position

Restricted stock units following transaction 110,866 restricted stock units Simon Irish’s reported position

Indirect common shares through an LLC 2,818,520 shares Simon Irish’s reported position

Indirect common shares through an IRA 52,255 shares Simon Irish’s reported position

Key Terms

Restricted Stock Units, pro rata, accelerated vesting

3 terms

Restricted Stock Units financial

"Each restricted stock unit represents a contingent right to receive one share of common stock."

Restricted stock units are a type of company reward where employees are promised shares of stock, but they only fully own these shares after meeting certain conditions, like staying with the company for a set time. They matter because they can become valuable assets and are often used to motivate employees to help the company succeed.

pro rata financial

"vest pro rata over a three year period following the grant date"

Pro rata means dividing or distributing something proportionally based on a specific factor, such as ownership or contribution. For example, if an investor owns 10% of a company, they would receive 10% of any dividends or benefits allocated. This approach ensures everyone gets their fair share relative to their stake or input, helping investors understand how benefits, costs, or responsibilities are fairly shared.

accelerated vesting financial

"accelerated vesting in certain events"

A contract feature that makes stock awards, options, or restricted shares become owned or exercisable earlier than the original schedule. It shortens or cancels the waiting period so recipients can sell, transfer, or exercise their equity sooner — think of a timed lock that is unlocked ahead of schedule. It matters to investors because it changes when shares enter the market, who controls them, and how much dilution or ownership concentration happens.

FAQ

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

How many IMSR shares did CEO Simon Irish receive from his RSUs?

On October 28, 2026, Simon Irish exercised/converted 55,432 restricted stock units, corresponding to the acquisition of 55,432 common shares.

How do Simon Irish’s IMSR RSUs vest?

The restricted stock units vest pro rata over three years following the grant date, subject to continued employment through each applicable vesting date, with accelerated vesting in certain events.

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

Form 4 Insider Transactions: What Each Field Means →

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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).

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^*

Irish Simon

(Last)

(First)

(Middle)

C/O TERRESTRIAL ENERGY INC.

2730 W. TYVOLA ROAD, SUITE 100

(Street)

CHARLOTTE

NORTH CAROLINA

28217

(City)

(State)

(Zip)

UNITED STATES

(Country)

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

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

X	Director	10% Owner
X	Officer (give title below)	Other (specify below)
	Chief Executive Officer

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
10/28/2026

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)
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	Code	V	Amount	(A) or (D)	Price		6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
Common Stock	10/28/2026		M		55,432⁽¹⁾	A	$0	2,879,846	D
Common Stock								2,818,520	I	Through LLC
Common Stock								52,255	I	Through IRA

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)
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)	Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares	8. Price of Derivative Security (Instr. 5)		10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
Restricted Stock Units	⁽²⁾	10/28/2026		M			55,432	⁽³⁾	⁽³⁾	Common Stock	55,432	$0	110,866	D

Explanation of Responses:

1. Represents shares of common stock subject to vested portion of restricted stock unit award.

2. Each restricted stock unit represents a contingent right to receive one share of common stock.

3. The restricted stock units vest pro rata over a three year period following the grant date, subject to Mr. Irish's continued employment through each applicable vesting date and accelerated vesting in certain events.

	/s/ Brian Thrasher, as Attorney-in-Fact	10/30/2026
	** 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)

Source: View Original Filing on SEC EDGAR