# EDGAR Filing Document

**Accession Number:** 0002088256
**File Stem:** 0001213900-26-034087
**Filing Date:** 2026-3
**Character Count:** 7438
**Document Hash:** 619b19d48cd56b22fd9c2f382eaf4e32
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001213900-26-034087.hdr.sgml**: 20260325

**ACCESSION NUMBER**: 0001213900-26-034087

**CONFORMED SUBMISSION TYPE**: 4

**PUBLIC DOCUMENT COUNT**: 1

**CONFORMED PERIOD OF REPORT**: 20260319

**FILED AS OF DATE**: 20260325

**DATE AS OF CHANGE**: 20260325

**REPORTING-OWNER**: 

**OWNER DATA:**
- **COMPANY CONFORMED NAME:** Tan Si-Hui
- **CENTRAL INDEX KEY:** 0002120880

**ORGANIZATION NAME:**

**FILING VALUES:**
- **FORM TYPE:** 4
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 001-43203
- **FILM NUMBER:** 26792714

**MAIL ADDRESS:**
- **ADDRESS IS A NON US LOCATION:** YES
- **STREET 1:** 24 FITZWILLIAM PLACE
- **CITY:** DUBLIN
- **PROVINCE COUNTRY:** L2
- **ZIP:** D02 T296
**ISSUER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Horizon Quantum Holdings Ltd.
- **CENTRAL INDEX KEY:** 0002088256
- **STANDARD INDUSTRIAL CLASSIFICATION:** SERVICES-COMPUTER PROGRAMMING SERVICES [7371]
- **ORGANIZATION NAME:** 06 Technology
- **EIN:** 000000000
- **STATE OF INCORPORATION:** U0
- **FISCAL YEAR END:** 1231

**BUSINESS ADDRESS:**
- **ADDRESS IS A NON US LOCATION:** YES
- **STREET 1:** ALICE@MEDIAOPOLIS
- **STREET 2:** 29 MEDIA CIRCLE #05-22
- **CITY:** SINGAPORE
- **PROVINCE COUNTRY:** U0
- **ZIP:** 138565
- **BUSINESS PHONE:** 6581015024

**MAIL ADDRESS:**
- **ADDRESS IS A NON US LOCATION:** YES
- **STREET 1:** ALICE@MEDIAOPOLIS
- **STREET 2:** 29 MEDIA CIRCLE #05-22
- **CITY:** SINGAPORE
- **PROVINCE COUNTRY:** U0
- **ZIP:** 138565

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** Horizon Quantum Holdings Pte. Ltd.
- **DATE OF NAME CHANGE:** 20251230

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** Rose Holdco Pte. Ltd.
- **DATE OF NAME CHANGE:** 20250924

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

## FORM 4

### STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

[ ] 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**<sup>*</sup><br>Tan Si-Hui<br><sub>(Last) (First) (Middle)</sub><br>C/O HORIZON QUANTUM HOLDINGS LTD.<br>29 MEDIA CIR. #05-22<br><sub>(Street)</sub><br>SINGAPORE, SINGAPORE 138565<br><sub>(City) (State) (Zip)</sub> | **3. Date of Earliest Transaction (Month/Day/Year)**<br>2026-03-19 | **5. Relationship of Reporting Person(s) to Issuer**<br>(Check all applicable)<br>[ ] Director [ ] 10% Owner<br>[X] Officer (give title below) [ ] Other (specify below)<br>_Chief Science Officer_ |
| **2. Issuer Name and Ticker or Trading Symbol**<br>Horizon Quantum Holdings Ltd. [ HQ ] | **4. If Amendment, Date of Original Filed (Month/Day/Year)**<br>  | **6. Individual or Joint/Group Filing (Check Applicable Line)**<br>[X] Form filed by One Reporting Person<br>[ ] Form filed by More than One Reporting Person |

---

## Table I - Non-Derivative Securities

---

|  |  |  |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 1. Title of Security | 2. Transaction Date | 2A. Deemed Execution Date | 3. Transaction Code (V) | 3. Transaction Code (V) | 4. Securities Acquired (A) or Disposed of (D) | 4. Securities Acquired (A) or Disposed of (D) | 4. Securities Acquired (A) or Disposed of (D) | 5. Amount of Securities Beneficially Owned | 6. Ownership Form | 7. Nature of Indirect Beneficial Ownership |
| 1. Title of Security | 2. Transaction Date | 2A. Deemed Execution Date | Code | V | Amount | (A) or (D) | Price | 5. Amount of Securities Beneficially Owned | 6. Ownership Form | 7. Nature of Indirect Beneficial Ownership |
|  |  |  |  |  |  |  |  |  |  |  |

---

## Table II - Derivative Securities

---

|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 1. Title of Derivative Security | 2. Conversion or Exercise Price | 3. Transaction Date | 3A. Deemed Execution Date | 4. Transaction Code (V) | 4. Transaction Code (V) | 5. Number of Derivative Securities Acquired (A) or Disposed of (D) | 5. Number of Derivative Securities Acquired (A) or Disposed of (D) | 6. Date Exercisable and Expiration Date | 6. Date Exercisable and Expiration Date | 7. Title and Amount of Underlying Securities | 7. Title and Amount of Underlying Securities | 8. Price of Derivative Security | 9. Number of Derivative Securities Beneficially Owned | 10. Ownership Form | 11. Nature of Indirect Beneficial Ownership |
| 1. Title of Derivative Security | 2. Conversion or Exercise Price | 3. Transaction Date | 3A. Deemed Execution Date | Code | V | (A) | (D) | Date Exercisable | Expiration Date | Title | Amount or Number of Shares | 8. Price of Derivative Security | 9. Number of Derivative Securities Beneficially Owned | 10. Ownership Form | 11. Nature of Indirect Beneficial Ownership |
| Stock Option (Right to Buy) | 0.15<sup>(1)</sup> | 2026-03-19<sup>(2)</sup> |  | A |  | 500000<sup>(1)</sup> |  | <sup>(3)</sup> | 2032-03-01 | Class A Ordinary Shares | 1217494<sup>(1)</sup> | <sup>(4)</sup> | 500000 | D |  |

---

### Footnotes:

(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.

**Signature:** /s/ Si-Hui Tan  
**Date:** 2026-03-25

### Remarks:

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.**