Horizon Space Acquisition I Corp.

Item 1.01. Entry into a Material Definitive Agreement. The disclosures set forth under Item 2.03 are incorporated by reference.

Item 2.03. Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant. On July 20, 2026, Horizon Space Acquisition I Corp., a Cayman Islands exempted company (the “Company”) issued an unsecured promissory note (the “Note”) in the principal amount of $500,000 to Horizon Space Acquisition I Sponsor Corp., a Cayman Islands company, the sponsor of the Company (the “Sponsor”). The proceeds of the Note, which may be drawn down from time to time until the Company consummates its initial business combination, will be used as general working capital purposes. The Note bears no interest and is payable in full upon the earlier to occur of (i) the consummation of the Company’s business combination or (ii) the date of expiry of the term of the Company (the “Maturity Date”). The following shall constitute an event of default: (i) a failure to pay the principal within five business days of the Maturity Date; (ii) the commencement of a voluntary or involuntary bankruptcy action, (iii) the breach of the Company’s obligations thereunder; (iv) any cross defaults; (v) an enforcement proceedings against the Company; and (vi) any unlawfulness and invalidity in connection with the performance of the obligations thereunder, in which case the Note may be accelerated. The payee of the Note, the Sponsor, or its registered assignees or successors in interest (the “Payee”), has the right, but not the obligation, to convert the Note, in whole or in part, respectively, into private units (the “Units”) of the Company, each consisting of one ordinary share, par value $0.0001 per share (the “Ordinary Share”), one warrant, and one right to receive one-tenth (1/10) of one Ordinary Share upon the consummation of a business combination, as described in the prospectus of the Company (File No: 333-268578), by providing the Company with written notice of the intention to convert at least two business days prior to the closing of the business combination. The number of Units to be received by the Payee in connection with such conversion shall be an amount determined by dividing (x) the sum of the outstanding principal amount payable to the payee by (y) $10.00. The issuance of the Note was made pursuant to the exemption from registration contained in Section 4(a)(2) of the Securities Act of 1933, as amended. A copy of the Note is attached as Exhibit 10.1 to this Current Report on Form 8-K and is incorporated herein by reference. The foregoing description of the Note does not purport to be complete and is subject to, and is qualified in its entirety by, the full text of the Note. Item 3.02. Unregistered Sales of Equity Securities. The information disclosed under Item 2.03 of this Current Report on Form 8-K is incorporated by reference into this Item 3.02 to the extent required herein. The Units (and the underlying securities) issuable upon conversion of the Note, if any, (1) may not, subject to certain limited exceptions, be transferable or salable by the Payee until the completion of the Company’s initial business combination and (2) are entitled to registration rights.

Item 3.02. Unregistered Sales of Equity Securities. The information disclosed under Item 2.03 of this Current Report on Form 8-K is incorporated by reference into this Item 3.02 to the extent required herein. The Units (and the underlying securities) issuable upon conversion of the Note, if any, (1) may not, subject to certain limited exceptions, be transferable or salable by the Payee until the completion of the Company’s initial business combination and (2) are entitled to registration rights.