Statement of Changes in Beneficial Ownership (Form 4)

FORM 4 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 that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN 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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(Print or Type Responses)

1. Name and Address of Reporting Person * Tan Si-Hui 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 (Last) (First) (Middle) C/O HORIZON QUANTUM HOLDINGS LTD., 29 MEDIA CIR. #05-22 3. Date of Earliest Transaction (Month/Day/Year) 03/19/2026 (Street) SINGAPORE 138565 4. If Amendment, Date 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 (City) (State) (Zip) 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 Class A Ordinary Shares 08/20/2026(1) A 3,600(1) A $ 0 (2) 3,600 I By Spouse Class A Ordinary Shares 09/12/2026(3) M 5,728(4) A $ 0 (4) 5,728 D Class A Ordinary Shares 09/12/2026(5) D 2,991(5) D $15.22(5) 2,737 D

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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 Underlying Securities (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 of Derivative Security: 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)

$2.88(6)

03/19/2026(7)

A

55,000(7)

(7)

02/01/2035

Class A Ordinary Shares

133,924(6)

(8)

55,000

I

By Spouse

Restricted Stock Unit

$ 0 (2)

06/12/2026

A

91,659(4)

(4)

(4)

Class A Ordinary Shares

91,659(4)

$ 0

91,659

D

Restricted Stock Unit

$ 0 (2)

09/12/2026

M

5,728(3)

(3)(4)

(4)

Class A Ordinary Shares

5,728

$ 0

85,931

D

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
Tan Si-Hui C/O HORIZON QUANTUM HOLDINGS LTD. 29 MEDIA CIR. #05-22 SINGAPORE 138565			Chief Science Officer

Signatures

/s/ Si-Hui Tan		09/15/2026
**Signature of Reporting Person		Date

Explanation of Responses:

*	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).
(1)	On August 20, 2026 (the "August Grant Date"), Dr. Tan's spouse was granted a total of unvested 3,600 RSUs. The RSUs granted to Dr. Tan's spouse are subject to his continued employment with the Company and vest in accordance with the following schedule: One quarter (1/4) of the total number of RSUs vest on the first anniversary of the August Grant Date with the remaining three quarters (3/4) vesting in twelve approximately equal quarterly installments on 20th day of each fiscal quarter.
(2)	Each restricted stock unit ("RSU") represents a contingent right to receive one Class A ordinary share, with no par value ("Class A Ordinary Share"), of Horizon Quantum Holdings Ltd. (the "Company") upon vesting, for no consideration.
(3)	On September 12, 2026, 5,728 of Dr. Tan's RSU's vested.
(4)	On June 12, 2026 (the "June Grant Date"), Dr. Tan was granted a total of 91,659 unvested RSUs. The RSUs granted to Dr. Tan vest in sixteen approximately equal installments on successive quarterly anniversaries of the June Grant Date and are subject to Dr. Tan's continued employment with the Company through each applicable vesting date.
(5)	The reported disposition to the Company reflects the settlement in cash of a portion of the RSUs which vested on September 12, 2026, at a price per ordinary share of $15.22, the last reported sales price of the Company's Class A Ordinary Shares on September 11, 2026.
(6)	Each stock option has an exercise price of $2.88 and is exercisable for approximately 2.43499 Class A Ordinary Shares of the Company. In aggregate, Dr. Tan's spouse's stock options, once fully vested, are exercisable for 133,924 Class A Ordinary Shares of the Company.
(7)	Of the 55,000 stock options, 37,811 stock options are currently fully vested and exercisable. The remaining stock options vest in five approximately equal quarterly installments beginning on November 20, 2026, subject to Dr. Tan's spouse's continued employment with the Company.
(8)	As a result of the closing of the Company's business combination on March 19, 2026, Dr. Tan's spouse's 55,000 Legacy Horizon stock options were exchanged for 55,000 stock options of the Company of an equivalent economic value, with an exercise price per Class A Ordinary Share of $2.88.

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