Horizon Quantum CSO granted 500,000 stock options

Tan Si-Hui reported acquisition or exercise transactions in this Form 4 filing.

Rhea-AI Filing Summary

Tan Si-Hui reported acquisition or exercise transactions in this Form 4 filing.

Horizon Quantum Holdings Ltd. reported that Chief Science Officer Dr. Tan Si-Hui received a grant of 500,000 stock options on March 19, 2026. Each option is exercisable at $0.15 per Class A Ordinary Share and is exercisable for 2.43499 Class A Ordinary Shares, covering 1,217,494 underlying Class A Ordinary Shares.

These fully vested options were not a new cash purchase but were issued in exchange for Dr. Tan’s 500,000 Legacy Horizon stock options as part of the closing of the Business Combination under the Business Combination Agreement. Following this exchange, Dr. Tan holds 500,000 Company stock options directly.

Insider Trade Summary

Grant/Award: 500,000 shares

Grant/Award 1 txn

Insider Tan Si-Hui

Role Chief Science Officer

Type	Security	Shares	Price	Value
Grant/Award	Stock Option (Right to Buy)	500,000	$0.00	$0.00

Holdings After Transaction: Stock Option (Right to Buy) — 500,000 contracts (Direct)

Footnotes (4)

1. F1. Each stock option is exercisable for 2.43499 Class A Ordinary Shares of Horizon Quantum Holdings Ltd. (the "Company") at a price per share of $0.15.
2. F2. Stock options received as part of the business combination (the "Business Combination") contemplated by the Business Combination Agreement, dated as of September 9, 2025 (the "BCA"), by and among Horizon Quantum Computing Pte. Ltd. ("Legacy Horizon"), dMY Squared Technology Group, Inc., the Company and certain other parties, as described in the Registration Statement on Form F-4, as amended and supplemented (File No. 333-292737), initially filed with the U.S. Securities and Exchange Commission on January 14, 2026, and declared effective on February 17, 2026. Upon the closing of the Business Combination on March 19, 2026, Dr. Tan's stock options exercisable for Legacy Horizon ordinary shares awarded by Legacy Horizon were exchanged for substitute stock option awards of the Company of an equivalent economic value.
3. F3. The stock options held by Dr. Tan are fully vested and exercisable.
4. F4. Pursuant to the BCA and as a result of the closing of the Business Combination, Dr. Tan's 500,000 Legacy Horizon stock options were exchanged for 500,000 stock options of the Company of an equivalent economic value, with an exercise price per Class A Ordinary Share of $0.15.

FAQ

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

What insider transaction did Horizon Quantum (HQ) report for Dr. Tan Si-Hui?

Horizon Quantum reported that Chief Science Officer Dr. Tan Si-Hui received 500,000 stock options on March 19, 2026. These options were issued as an exchange for prior Legacy Horizon options in connection with the closing of the Business Combination.

What are the key terms of Dr. Tan’s new Horizon Quantum (HQ) stock options?

Dr. Tan’s stock options are fully vested, exercisable at $0.15 per Class A Ordinary Share, and expire on March 1, 2032. Each option is exercisable for 2.43499 Class A Ordinary Shares, covering a total of 1,217,494 underlying shares.

How were Dr. Tan’s Legacy Horizon options treated in the Horizon Quantum (HQ) Business Combination?

Upon closing of the Business Combination on March 19, 2026, Dr. Tan’s 500,000 Legacy Horizon stock options were exchanged for 500,000 Horizon Quantum stock options. The company states these substitute options have an equivalent economic value to the original awards.

Is Dr. Tan’s Horizon Quantum (HQ) option grant a new purchase of shares?

The filing describes the transaction as stock options received and exchanged, not an open-market purchase of shares. It is a compensation-related grant and substitution of pre-existing Legacy Horizon options following the Business Combination, with no buy or sell transaction reported.

How many Horizon Quantum (HQ) options does Dr. Tan hold after this transaction?

After the exchange, Dr. Tan holds 500,000 Horizon Quantum stock options directly, as reported in the filing. These options are fully vested and exercisable and relate to 1,217,494 underlying Class A Ordinary Shares at an exercise price of $0.15 per share.

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

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Accepted by SEC EDGAR 03/25/2026 - 04:21 PM Learn about SEC filing dates

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
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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^*

Tan Si-Hui

(Last) (First) (Middle)

C/O HORIZON QUANTUM HOLDINGS LTD.

29 MEDIA CIR. #05-22

(Street)

SINGAPORE 138565

(City) (State) (Zip)

SINGAPORE

(Country)

2. Issuer Name and Ticker or Trading Symbol
Horizon Quantum Holdings Ltd. [ HQ ]

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

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

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
03/19/2026

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)
			Code	V	Amount	(A) or (D)	Price

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
Stock Option (Right to Buy)	$0.15(1)	03/19/2026(2)		A		500,000(1)		(3)	03/01/2032	Class A Ordinary Shares	1,217,494(1)	(4)	500,000	D

Explanation of Responses:

1. Each stock option is exercisable for 2.43499 Class A Ordinary Shares of Horizon Quantum Holdings Ltd. (the "Company") at a price per share of $0.15.

2. Stock options received as part of the business combination (the "Business Combination") contemplated by the Business Combination Agreement, dated as of September 9, 2025 (the "BCA"), by and among Horizon Quantum Computing Pte. Ltd. ("Legacy Horizon"), dMY Squared Technology Group, Inc., the Company and certain other parties, as described in the Registration Statement on Form F-4, as amended and supplemented (File No. 333-292737), initially filed with the U.S. Securities and Exchange Commission on January 14, 2026, and declared effective on February 17, 2026. Upon the closing of the Business Combination on March 19, 2026, Dr. Tan's stock options exercisable for Legacy Horizon ordinary shares awarded by Legacy Horizon were exchanged for substitute stock option awards of the Company of an equivalent economic value.

3. The stock options held by Dr. Tan are fully vested and exercisable.

4. Pursuant to the BCA and as a result of the closing of the Business Combination, Dr. Tan's 500,000 Legacy Horizon stock options were exchanged for 500,000 stock options of the Company of an equivalent economic value, with an exercise price per Class A Ordinary Share of $0.15.

	/s/ Si-Hui Tan	03/25/2026
	** 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.
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* Form 4: SEC 1474 (03-26)