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SEC source: 0001213900-26-100283 · ownership.xml · derivative · entry 4

Fitzsimons Catherine Michele · CIK 0002123065 · CL and CO

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 32,224

Underlying: Class A Ordinary Shares · 2,148 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F2 · derivative.exercise_price: On June 12, 2026 (the "Grant Date"), Ms. Fitzsimons was granted a total of 34,372 unvested restricted stock units ("RSUs"), each representing 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.. The RSUs granted to Ms. Fitzsimons vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Ms. Fitzsimons's continued employment with the Company through each applicable vesting date.

F1 · shares: On September 12, 2026, 2,148 of Ms. Fitzsimons's RSU's vested.

F1 · derivative.exercise_date: On September 12, 2026, 2,148 of Ms. Fitzsimons's RSU's vested.

F2 · derivative.exercise_date: On June 12, 2026 (the "Grant Date"), Ms. Fitzsimons was granted a total of 34,372 unvested restricted stock units ("RSUs"), each representing 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.. The RSUs granted to Ms. Fitzsimons vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Ms. Fitzsimons's continued employment with the Company through each applicable vesting date.

F2 · derivative.expiration_date: On June 12, 2026 (the "Grant Date"), Ms. Fitzsimons was granted a total of 34,372 unvested restricted stock units ("RSUs"), each representing 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.. The RSUs granted to Ms. Fitzsimons vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Ms. Fitzsimons's continued employment with the Company through each applicable vesting date.

SEC source: 0001213900-26-100283 · ownership.xml · nonDerivative · entry 2

Fitzsimons Catherine Michele · CIK 0002123065 · CL and CO

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 1,026

F1 · date: On September 12, 2026, 2,148 of Ms. Fitzsimons's RSU's vested.

F3 · shares: 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.

F3 · price: 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.

SEC source: 0001213900-26-100283 · ownership.xml · nonDerivative · entry 1

Fitzsimons Catherine Michele · CIK 0002123065 · CL and CO

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 2,148

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · date: On September 12, 2026, 2,148 of Ms. Fitzsimons's RSU's vested.

F1 · shares: On September 12, 2026, 2,148 of Ms. Fitzsimons's RSU's vested.

F2 · price: On June 12, 2026 (the "Grant Date"), Ms. Fitzsimons was granted a total of 34,372 unvested restricted stock units ("RSUs"), each representing 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.. The RSUs granted to Ms. Fitzsimons vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Ms. Fitzsimons's continued employment with the Company through each applicable vesting date.

SEC source: 0001213900-26-100281 · ownership.xml · derivative · entry 4

Gould Greg · CIK 0002120154 · Chief Financial Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 51,558

Underlying: Class A Ordinary Shares · 3,437 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F2 · derivative.exercise_price: On June 12, 2026 (the "Grant Date"), Mr. Gould was granted a total of 54,995 unvested restricted stock unites ("RSUs"), each representing 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.. The RSUs granted to Mr. Gould vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Mr. Gould's continued employment with the Company through each applicable vesting date.

F1 · shares: On September 12, 2026, 3,437 of Mr. Gould's RSU's vested.

F1 · derivative.exercise_date: On September 12, 2026, 3,437 of Mr. Gould's RSU's vested.

F2 · derivative.exercise_date: On June 12, 2026 (the "Grant Date"), Mr. Gould was granted a total of 54,995 unvested restricted stock unites ("RSUs"), each representing 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.. The RSUs granted to Mr. Gould vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Mr. Gould's continued employment with the Company through each applicable vesting date.

F2 · derivative.expiration_date: On June 12, 2026 (the "Grant Date"), Mr. Gould was granted a total of 54,995 unvested restricted stock unites ("RSUs"), each representing 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.. The RSUs granted to Mr. Gould vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Mr. Gould's continued employment with the Company through each applicable vesting date.

SEC source: 0001213900-26-100281 · ownership.xml · nonDerivative · entry 2

Gould Greg · CIK 0002120154 · Chief Financial Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 2,165

F1 · date: On September 12, 2026, 3,437 of Mr. Gould's RSU's vested.

F3 · shares: 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.

F3 · price: 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.

SEC source: 0001213900-26-100281 · ownership.xml · nonDerivative · entry 1

Gould Greg · CIK 0002120154 · Chief Financial Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 3,437

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · date: On September 12, 2026, 3,437 of Mr. Gould's RSU's vested.

F1 · shares: On September 12, 2026, 3,437 of Mr. Gould's RSU's vested.

F2 · price: On June 12, 2026 (the "Grant Date"), Mr. Gould was granted a total of 54,995 unvested restricted stock unites ("RSUs"), each representing 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.. The RSUs granted to Mr. Gould vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Mr. Gould's continued employment with the Company through each applicable vesting date.

SEC source: 0001213900-26-100280 · ownership.xml · derivative · entry 6

Tan Si-Hui · CIK 0002120880 · Chief Science Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 85,931

Underlying: Class A Ordinary Shares · 5,728 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F2 · derivative.exercise_price: 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.

F3 · shares: On September 12, 2026, 5,728 of Dr. Tan's RSU's vested.

F3 · derivative.exercise_date: On September 12, 2026, 5,728 of Dr. Tan's RSU's vested.

F4 · derivative.exercise_date: 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.

F4 · derivative.expiration_date: 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.

SEC source: 0001213900-26-100280 · ownership.xml · nonDerivative · entry 3

Tan Si-Hui · CIK 0002120880 · Chief Science Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 2,737

F5 · date: 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.

F5 · shares: 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.

F5 · price: 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.

SEC source: 0001213900-26-100280 · ownership.xml · nonDerivative · entry 2

Tan Si-Hui · CIK 0002120880 · Chief Science Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 5,728

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F3 · date: On September 12, 2026, 5,728 of Dr. Tan's RSU's vested.

F4 · shares: 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.

F4 · price: 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.

SEC source: 0001213900-26-100279 · ownership.xml · derivative · entry 4

Fitzsimons Joseph Francis · CIK 0002122720 · Director · Chief Executive Officer · 10% owner

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 214,827

Underlying: Class A Ordinary Shares · 14,321 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F2 · derivative.exercise_price: On June 12, 2026 (the "Grant Date"), Dr. Fitzsimons was granted a total of 229,148 unvested restricted stock units ("RSUs"), each representing 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. The RSUs granted to Dr. Fitzsimons vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Dr. Fitzsimons's continued employment with the Company through each applicable vesting date.

F1 · shares: On September 12, 2026, 14,321 of Dr. Fitzsimons's RSU's vested.

F1 · derivative.exercise_date: On September 12, 2026, 14,321 of Dr. Fitzsimons's RSU's vested.

F2 · derivative.exercise_date: On June 12, 2026 (the "Grant Date"), Dr. Fitzsimons was granted a total of 229,148 unvested restricted stock units ("RSUs"), each representing 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. The RSUs granted to Dr. Fitzsimons vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Dr. Fitzsimons's continued employment with the Company through each applicable vesting date.

F2 · derivative.expiration_date: On June 12, 2026 (the "Grant Date"), Dr. Fitzsimons was granted a total of 229,148 unvested restricted stock units ("RSUs"), each representing 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. The RSUs granted to Dr. Fitzsimons vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Dr. Fitzsimons's continued employment with the Company through each applicable vesting date.

SEC source: 0001213900-26-100279 · ownership.xml · nonDerivative · entry 2

Fitzsimons Joseph Francis · CIK 0002122720 · Director · Chief Executive Officer · 10% owner

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 10,883

F1 · date: On September 12, 2026, 14,321 of Dr. Fitzsimons's RSU's vested.

F3 · shares: 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.

F3 · price: 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.

SEC source: 0001213900-26-100279 · ownership.xml · nonDerivative · entry 1

Fitzsimons Joseph Francis · CIK 0002122720 · Director · Chief Executive Officer · 10% owner

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 14,321

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · date: On September 12, 2026, 14,321 of Dr. Fitzsimons's RSU's vested.

F1 · shares: On September 12, 2026, 14,321 of Dr. Fitzsimons's RSU's vested.

F2 · price: On June 12, 2026 (the "Grant Date"), Dr. Fitzsimons was granted a total of 229,148 unvested restricted stock units ("RSUs"), each representing 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. The RSUs granted to Dr. Fitzsimons vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Dr. Fitzsimons's continued employment with the Company through each applicable vesting date.

SEC source: 0001213900-26-100280 · ownership.xml · nonDerivative · entry 1

Tan Si-Hui · CIK 0002120880 · Chief Science Officer

10b5-1 filing: No plan indicated

Ownership: Indirect · By Spouse

Disclosed balance after: 3,600

F1 · date: 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.

F1 · shares: 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.

F2 · price: 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.

SEC source: 0001213900-26-100297 · ownership.xml · derivative · entry 1

Chew Qian Yi Amanda · CIK 0002148016 · Chief Product Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 17,857

Underlying: Class A Ordinary Shares · 17,857 shares

Expires not disclosed

F1 · derivative.exercise_price: 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.

F1 · shares: 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.

F1 · price: 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.

F1 · derivative.exercise_date: 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.

F2 · derivative.expiration_date: On August 17, 2026 (the "Grant Date"), Ms. Chew was granted a total of unvested 17,857 RSUs. The RSUs granted to Ms. Chew vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Ms. Chew's continued employment with the Company through each applicable vesting date.

F2 · derivative.underlying_shares: On August 17, 2026 (the "Grant Date"), Ms. Chew was granted a total of unvested 17,857 RSUs. The RSUs granted to Ms. Chew vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Ms. Chew's continued employment with the Company through each applicable vesting date.

SEC source: 0001213900-26-100283 · ownership.xml · derivative · entry 3

Fitzsimons Catherine Michele · CIK 0002123065 · CL and CO

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 34,372

Underlying: Class A Ordinary Shares · 34,372 shares

Expires not disclosed

F2 · derivative.exercise_price: On June 12, 2026 (the "Grant Date"), Ms. Fitzsimons was granted a total of 34,372 unvested restricted stock units ("RSUs"), each representing 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.. The RSUs granted to Ms. Fitzsimons vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Ms. Fitzsimons's continued employment with the Company through each applicable vesting date.

F2 · shares: On June 12, 2026 (the "Grant Date"), Ms. Fitzsimons was granted a total of 34,372 unvested restricted stock units ("RSUs"), each representing 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.. The RSUs granted to Ms. Fitzsimons vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Ms. Fitzsimons's continued employment with the Company through each applicable vesting date.

F2 · derivative.exercise_date: On June 12, 2026 (the "Grant Date"), Ms. Fitzsimons was granted a total of 34,372 unvested restricted stock units ("RSUs"), each representing 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.. The RSUs granted to Ms. Fitzsimons vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Ms. Fitzsimons's continued employment with the Company through each applicable vesting date.

F2 · derivative.expiration_date: On June 12, 2026 (the "Grant Date"), Ms. Fitzsimons was granted a total of 34,372 unvested restricted stock units ("RSUs"), each representing 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.. The RSUs granted to Ms. Fitzsimons vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Ms. Fitzsimons's continued employment with the Company through each applicable vesting date.

F2 · derivative.underlying_shares: On June 12, 2026 (the "Grant Date"), Ms. Fitzsimons was granted a total of 34,372 unvested restricted stock units ("RSUs"), each representing 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.. The RSUs granted to Ms. Fitzsimons vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Ms. Fitzsimons's continued employment with the Company through each applicable vesting date.

SEC source: 0001213900-26-100281 · ownership.xml · derivative · entry 3

Gould Greg · CIK 0002120154 · Chief Financial Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 54,995

Underlying: Class A Ordinary Shares · 54,995 shares

Expires not disclosed

F2 · derivative.exercise_price: On June 12, 2026 (the "Grant Date"), Mr. Gould was granted a total of 54,995 unvested restricted stock unites ("RSUs"), each representing 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.. The RSUs granted to Mr. Gould vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Mr. Gould's continued employment with the Company through each applicable vesting date.

F2 · shares: On June 12, 2026 (the "Grant Date"), Mr. Gould was granted a total of 54,995 unvested restricted stock unites ("RSUs"), each representing 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.. The RSUs granted to Mr. Gould vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Mr. Gould's continued employment with the Company through each applicable vesting date.

F2 · derivative.exercise_date: On June 12, 2026 (the "Grant Date"), Mr. Gould was granted a total of 54,995 unvested restricted stock unites ("RSUs"), each representing 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.. The RSUs granted to Mr. Gould vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Mr. Gould's continued employment with the Company through each applicable vesting date.

F2 · derivative.expiration_date: On June 12, 2026 (the "Grant Date"), Mr. Gould was granted a total of 54,995 unvested restricted stock unites ("RSUs"), each representing 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.. The RSUs granted to Mr. Gould vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Mr. Gould's continued employment with the Company through each applicable vesting date.

F2 · derivative.underlying_shares: On June 12, 2026 (the "Grant Date"), Mr. Gould was granted a total of 54,995 unvested restricted stock unites ("RSUs"), each representing 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.. The RSUs granted to Mr. Gould vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Mr. Gould's continued employment with the Company through each applicable vesting date.

SEC source: 0001213900-26-100280 · ownership.xml · derivative · entry 5

Tan Si-Hui · CIK 0002120880 · Chief Science Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 91,659

Underlying: Class A Ordinary Shares · 91,659 shares

Expires not disclosed

F2 · derivative.exercise_price: 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.

F4 · shares: 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.

F4 · derivative.exercise_date: 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.

F4 · derivative.expiration_date: 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.

F4 · derivative.underlying_shares: 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.

SEC source: 0001213900-26-100279 · ownership.xml · derivative · entry 3

Fitzsimons Joseph Francis · CIK 0002122720 · Director · Chief Executive Officer · 10% owner

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 229,148

Underlying: Class A Ordinary Shares · 229,148 shares

Expires not disclosed

F2 · derivative.exercise_price: On June 12, 2026 (the "Grant Date"), Dr. Fitzsimons was granted a total of 229,148 unvested restricted stock units ("RSUs"), each representing 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. The RSUs granted to Dr. Fitzsimons vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Dr. Fitzsimons's continued employment with the Company through each applicable vesting date.

F2 · shares: On June 12, 2026 (the "Grant Date"), Dr. Fitzsimons was granted a total of 229,148 unvested restricted stock units ("RSUs"), each representing 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. The RSUs granted to Dr. Fitzsimons vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Dr. Fitzsimons's continued employment with the Company through each applicable vesting date.

F2 · derivative.exercise_date: On June 12, 2026 (the "Grant Date"), Dr. Fitzsimons was granted a total of 229,148 unvested restricted stock units ("RSUs"), each representing 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. The RSUs granted to Dr. Fitzsimons vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Dr. Fitzsimons's continued employment with the Company through each applicable vesting date.

F2 · derivative.expiration_date: On June 12, 2026 (the "Grant Date"), Dr. Fitzsimons was granted a total of 229,148 unvested restricted stock units ("RSUs"), each representing 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. The RSUs granted to Dr. Fitzsimons vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Dr. Fitzsimons's continued employment with the Company through each applicable vesting date.

F2 · derivative.underlying_shares: On June 12, 2026 (the "Grant Date"), Dr. Fitzsimons was granted a total of 229,148 unvested restricted stock units ("RSUs"), each representing 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. The RSUs granted to Dr. Fitzsimons vest in sixteen approximately equal installments on successive quarterly anniversaries of the Grant Date and are subject to Dr. Fitzsimons's continued employment with the Company through each applicable vesting date.

SEC source: 0001213900-26-100280 · ownership.xml · derivative · entry 4

Tan Si-Hui · CIK 0002120880 · Chief Science Officer

10b5-1 filing: No plan indicated

Ownership: Indirect · By Spouse

Disclosed balance after: 55,000

Underlying: Class A Ordinary Shares · 133,924 shares

Expires 2035-02-01

F6 · derivative.exercise_price: 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.

F7 · date: 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.

F7 · shares: 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.

F8 · price: 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.

F7 · derivative.exercise_date: 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.

F6 · derivative.underlying_shares: 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.

SEC source: 0001829126-26-002587 · ownership.xml · derivative · entry 3

You Harry L. · CIK 0001432602 · Director · 10% owner

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnote

Disclosed balance after: 2,884,660

Underlying: Class A Ordinary Shares · 2,884,660 shares

Expires 2031-03-19

F2 · price: In connection with the closing of the Business Combination, these warrants of the Issuer were issued pursuant to the terms of the Business Combination Agreement upon the exchange of 2,884,660 warrants of DMY. On the effective date of the Business Combination, the closing price of DMY's warrants was $2.69.

F3 · ownership.nature: dMY Squared Sponsor, LLC (the "Sponsor") Sponsor is the record holder of the securities reported herein. Harry L. You is the managing member of the Sponsor and has voting and investment discretion with respect to the securities held of record by the Sponsor. Each of the Sponsor and Mr. You is a "Reporting Person" and may be deemed to beneficially own the securities reported herein; however, each Reporting Person disclaims beneficial ownership of the securities reported herein, except to the extent of such Reporting Person's pecuniary interest therein. Solely for purposes of Section 16 of the Exchange Act, each Reporting Person may be deemed a "director by deputization".

SEC source: 0001829126-26-002587 · ownership.xml · nonDerivative · entry 1

You Harry L. · CIK 0001432602 · Director · 10% owner

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnote

Disclosed balance after: 1,163,484

F1 · price: In connection with the closing of the business combination (the "Business Combination") among Horizon Quantum Holdings Ltd. (the "Issuer"), Horizon Quantum Computing Pte. Ltd. ("Horizon"), and dMY Squared Technology Group, Inc. ("DMY"), these Class A ordinary shares of the Issuer were issued pursuant to the terms of the Business Combination Agreement, dated as of September 9, 2025, by and among the Issuer, Horizon, and DMY (the "Business Combination Agreement") upon the exchange of 1,163,484 shares of Class A common stock of DMY. On the effective date of the Business Combination, the closing price of DMY's Class A common stock was $13.50.

F3 · ownership.nature: dMY Squared Sponsor, LLC (the "Sponsor") Sponsor is the record holder of the securities reported herein. Harry L. You is the managing member of the Sponsor and has voting and investment discretion with respect to the securities held of record by the Sponsor. Each of the Sponsor and Mr. You is a "Reporting Person" and may be deemed to beneficially own the securities reported herein; however, each Reporting Person disclaims beneficial ownership of the securities reported herein, except to the extent of such Reporting Person's pecuniary interest therein. Solely for purposes of Section 16 of the Exchange Act, each Reporting Person may be deemed a "director by deputization".

SEC source: 0001213900-26-033688 · ownership.xml · nonDerivative · entry 1

Fitzsimons Joseph Francis · CIK 0002122720 · Director · Chief Executive Officer · 10% owner

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 19,744,585

F1 · security: Each Class B ordinary share, with no par value (the "Class B Ordinary Shares"), is convertible, at any time, in exchange for one Class A ordinary share, with no par value (the "Class A Ordinary Shares").

F2 · date: Class B Ordinary Shares, received on March 19, 2026, upon the closing of 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., Horizon Quantum Holdings Ltd. (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.

F3 · price: Pursuant to the BCA and as a result of the Business Combination, Dr. Fitzsimons exchanged his then outstanding 8,108,696 ordinary shares of Legacy Horizon for 19,744,585 Class B Ordinary Shares of the Company.

SEC source: 0001213900-26-034272 · ownership.xml · nonDerivative · entry 1

Lambert Danielle · CIK 0002120146 · Director

10b5-1 filing: No plan indicated

Ownership: Indirect · Penchant Family Holdings LLC

Disclosed balance after: 84,602

F1 · date: On March 6, 2026, dMY Squared Technology Group, Inc. ("dMY"), the Company, and Horizon Quantum Computing Pte. Ltd. entered into a subscription agreement with Penchant Family Holdings LLC, whereby the Company, upon the closing of the Company's business combination with dMY, would issue 84,602 shares of the Company's Class A ordinary shares, with no par value (the "Class A Ordinary Shares") to Penchant Family Holdings LLC at a price per share of $11.82, for an aggregate purchase price of approximately $1,000,000. The closing of the Company's business combination occurred on March 19, 2026, and the 84,602 Class A Ordinary Shares of the Company were sold to Penchant Family Holdings LLC on that date.

F1 · kind: On March 6, 2026, dMY Squared Technology Group, Inc. ("dMY"), the Company, and Horizon Quantum Computing Pte. Ltd. entered into a subscription agreement with Penchant Family Holdings LLC, whereby the Company, upon the closing of the Company's business combination with dMY, would issue 84,602 shares of the Company's Class A ordinary shares, with no par value (the "Class A Ordinary Shares") to Penchant Family Holdings LLC at a price per share of $11.82, for an aggregate purchase price of approximately $1,000,000. The closing of the Company's business combination occurred on March 19, 2026, and the 84,602 Class A Ordinary Shares of the Company were sold to Penchant Family Holdings LLC on that date.

F2 · ownership.direct: Penchant Family Holdings LLC is controlled by Penchant Holdings, Inc., its Managing Member, of which Danielle Lambert serves as its President.

F2 · ownership.nature: Penchant Family Holdings LLC is controlled by Penchant Holdings, Inc., its Managing Member, of which Danielle Lambert serves as its President.

SEC source: 0001213900-26-034087 · ownership.xml · derivative · entry 1

Tan Si-Hui · CIK 0002120880 · Chief Science Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 500,000

Underlying: Class A Ordinary Shares · 1,217,494 shares

Expires 2032-03-01

F1 · derivative.exercise_price: 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.

F2 · date: 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.

F1 · shares: 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.

F4 · price: 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.

F3 · derivative.exercise_date: The stock options held by Dr. Tan are fully vested and exercisable.

F1 · derivative.underlying_shares: 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.

SEC source: 0001213900-26-034065 · ownership.xml · derivative · entry 1

Gould Greg · CIK 0002120154 · Chief Financial Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 285,300

Underlying: Class A Ordinary Shares · 694,702 shares

Expires 2035-08-15

F1 · derivative.exercise_price: 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 $5.13.

F2 · date: 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, Mr. Gould'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, which are subject to a vesting schedule as further detailed in footnote 3.

F1 · shares: 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 $5.13.

F4 · price: Pursuant to the BCA and as a result of the closing of the Business Combination, Mr. Gould's 285,300 Legacy Horizon stock options were exchanged for 285,300 stock options of the Company of an equivalent economic value, with an exercise price per Class A Ordinary Share of $5.13.

F3 · derivative.exercise_date: The stock options held by Mr. Gould are subject to Mr. Gould's continued employment with the Company and vest quarterly in 16 equal installments, beginning on August 15, 2025. As of March 24, 2026, 35,662 stock options are fully vested and exercisable, with the remaining 249,638 stock options vesting in accordance with the forgoing schedule.

F1 · derivative.underlying_shares: 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 $5.13.