GigCapital9 Corp.

Item 1.01 Entry into Material Definitive Agreement. On January 26, 2026, GigCapital9 Corp., a Cayman Island exempted company (the “Company”), priced its initial public offering (the “IPO”) following the declaration of its registration statement on Form S-1 (File No. 333-291869), as amended (the “Registration Statement”) effective by the U.S. Securities and Exchange Commission (the “SEC”) on January 23, 2026. On January 27, 2026, the representative of the underwriters in the IPO served the Company written notice of the exercise of the over-allotment option in full. On January 28, 2026, the Company consummated the IPO of 25,300,000 units (the “Units”), including 3,300,000 Units as a result of the underwriters’ exercise in full of their over-allotment option. Each Unit consists of one Class A ordinary share of the Company, par value $0.0001 per share (each an “Ordinary Share”), and one right to receive one-fifth of an Ordinary Share (a “Public Right”), with each five rights entitling the holder thereof to receive one Ordinary Share upon the consummation of an initial business combination. The Units were sold at a price of $10.00 per Unit, generating gross proceeds to the Company of $253,000,000. In connection with the IPO, the Company entered into the following agreements previously filed as exhibits to the Company’s Registration Statement: An Underwriting Agreement, dated January 26, 2026, by and between the Company and D. Boral Capital LLC (“DBC”), acting as representative of the underwriters named therein, which contains customary representations and warranties and indemnification of the underwriters by the Company and is attached as Exhibit 1.1 hereto and incorporated herein by reference; A Rights Agreement, dated January 26, 2026, by and between the Company and Continental Stock Transfer & Trust Company, as rights agent, a copy of which is attached as Exhibit 4.1 hereto and incorporated herein by reference; An Insider Letter Agreement, dated January 26, 2026, by and among the Company, GigAcquisitions9 Corp. (the “Sponsor”), each of its officers and directors, DBC, and certain other security holders named therein, a copy of which is attached as Exhibit 10.1 hereto and incorporated herein by reference (the “Insider Letter Agreement”); A Registration Rights Agreement, dated January 26, 2026, by and among the Company, the Sponsor, and certain other security holders named therein, a copy of which is attached as Exhibit 10.2 hereto and incorporated herein by reference; An Investment Management Trust Agreement, dated January 26, 2026, by and between the Company and Continental Stock Transfer & Trust Company, as trustee, a copy of which is attached as Exhibit 10.3 hereto and incorporated herein by reference; An Administrative Services Agreement, dated January 26, 2026, by and between the Company and GigManagement, LLC, a copy of which is attached as Exhibit 10.4 hereto and incorporated herein by reference; An Indemnity Agreement, dated January 26, 2026, by and between the Company and Dr. Avi S. Katz, the Chief Executive Officer of the Company, a copy of which is attached as Exhibit 10.5 hereto and incorporated herein by reference; An Indemnity Agreement, dated January 26, 2026, by and between the Company and Dr. Raluca Dinu, a director of the Company, a copy of which is attached as Exhibit 10.6 hereto and incorporated herein by reference; An Indemnity Agreement, dated January 28, 2026, by and between the Company and Admiral (Ret.) David Ben-Bashat, a director of the Company, a copy of which is attached as Exhibit 10.7 hereto and incorporated herein by reference; An Indemnity Agreement, dated January 28, 2026, by and between the Company and Raanan I. Horowitz, a director of the Company, a copy of which is attached as Exhibit 10.8 hereto and incorporated herein by reference; An Indemnity Agreement, dated January 28, 2026, by and between the Company and Ambassador Adrian Zuckerman, a director of the Company, a copy of which is attached as Exhibit 10.9 hereto and incorporated herein by reference; An Indemnity Agreement, dated January 28, 2026, by and between the Company and Luis Machuca, a director of the Company, a copy of which is attached as Exhibit 10.10 hereto and incorporated herein by reference. An Indemnity Agreement, dated January 28, 2026, by and between the Company and Bryan Timm, a director of the Company, a copy of which is attached as Exhibit 10.11 hereto and incorporated herein by reference; An Indemnity Agreement, dated January 28, 2026, by and between the Company and Maj. General (Ret.) Avi Mizrachi, a director of the Company, a copy of which is attached as Exhibit 10.12 hereto and incorporated herein by reference; and An Indemnity Agreement, dated January 26, 2026, by and between the Company and Christine Marshall, the Chief Financial Officer of the Company, a copy of which is attached as Exhibit 10.13 hereto and incorporated herein by reference; The material terms of each of the foregoing agreements are described in the prospectus that forms a part of the Registration Statement, and the descriptions of such terms are incorporated herein by reference. Each of the foregoing agreements, are attached hereto as exhibits to this Current Report on Form 8-K, as enumerated below in the table set forth in response to Item 9.01.

Item 3.02 Unregistered Sales of Equity Securities. Simultaneously with the closing of the IPO, the Company completed the private sale and issuance of an aggregate of 107,500 units (the “Private Placement Units”) to the Sponsor, three of the Company’s directors, certain other GigCapital Global advisors and Lynrock Lake Master Fund LP at a price of $9.7374 per unit, generating gross proceeds to the Company of $1,046,771. Each Private Placement Unit consisted of one Ordinary Share and one right to receive one-fifth of an Ordinary Share, with each five rights entitling the holder thereof to receive one Ordinary Share upon the consummation of an initial business combination. Each such investor signed a unit purchase agreement with the Company, the material terms of which are set forth in the Registration Statement and incorporated by reference herein. Simultaneously with the closing of the IPO, the Company completed the private sale and issuance to certain non-managing investors (none of which are affiliated with any member of the Company’s management, the Sponsor or any other investor) of (i) an aggregate of 3,178,430 Class B ordinary shares of the Company, par value of $0.0001 per share (“Class B Ordinary Shares”) at a price of $0.023254 per share and (ii) an aggregate of 281,454 Private Placement Units at a price of $9.7374 per unit, generating gross proceeds to the Company of $2,814,541. Each such investor signed a subscription agreement with the Company, the materials terms of which are set forth in the Registration Statement and incorporated by reference herein.

Item 5.02 Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers. In connection with the IPO, on January 26, 2026, each of Dr. Avi S. Katz, Dr. Raluca Dinu and Christine Marshall, the Chief Financial Officer of the Company, entered into an indemnity agreement with the Company. When the election of Messrs. Zuckerman, Mizrachi, Machuca, Horowtiz, Ben-Bashat and Timm as directors of the Company became effective on January 28, 2026, each of them entered into an indemnity agreement with the Company. On January 26, 2026, all directors, director nominees and officers of the Company along with the Sponsor and certain other security holders named therein, entered into the Insider Letter Agreement. Other than the foregoing, none of the directors or officers of the Company is party to any arrangement or understanding with any person pursuant to which they were appointed as directors, nor are they party to any transactions required to be disclosed under Item 404(a) of Regulation S-K involving the Company. Copies of the Insider Letter Agreement and indemnity agreements are attached as Exhibits 10.1 and 10.5 through 10.13 hereto, respectively, and are incorporated herein by reference.

Item 5.03 Amendments to Articles of Incorporation or Bylaws; Change in Fiscal Year On January 26, 2026, in connection with the IPO, the Company adopted its First Amended and Restated Memorandum and Articles of Association (the “Amended and Restated Articles”), effective the same day. The terms of the Amended and Restated Articles are set forth in the Registration Statement and are incorporated herein by reference. A copy of the Amended and Restated Articles is attached as Exhibit 3.1 hereto and incorporated herein by reference.

Item 8.01 Other Events In connection with the IPO, Messrs. Horowitz, Timm and Zuckerman were appointed to the Audit Committee of the Company’s board of directors, with Mr. Timm serving as chair of the Audit Committee; Messrs. Horowitz, Timm and Machuca were appointed to the Compensation Committee of the Company’s board of directors, with Mr. Machuca serving as chair of the Compensation Committee; and Messrs. Ben-Bashat, Machuca and Horowitz were appointed to the Nominating and Corporate Governance Committee of the Company’s board of directors, with Mr. Horowitz serving as chair of the Nominating and Corporate Governance Committee. A total of $253,000,000, consisting of the entirety of the proceeds received by the Company from the IPO and private placement after deduction for commissions from the IPO, were placed in a U.S.-based trust account at JPMorgan Chase Bank, N.A. maintained by Continental Stock Transfer & Trust Company, acting as trustee. Except with respect to interest earned on the funds held in the trust account that may be released to the Company to pay its taxes, the funds in the trust account will not be released from the trust account until the earliest to occur of: (i) the completion of the Company’s initial business combination, (ii) the redemption of any public shares properly submitted in connection with the implementation by the directors of, following a shareholder vote, an amendment to the Company’s amended and restated memorandum and articles of association (A) to modify the substance or timing of our obligation to provide for the redemption of our public shares in connection with an initial business combination or to redeem 100% of our public shares if the Company has not consummated its initial business combination within 24 months from the closing of the offering or (B) with respect to any other provisions relating to shareholders’ rights or pre-initial business combination activity, and (iii) the redemption of public shares absent an initial business combination within 24 months from the closing of the offering. On January 26, 2026, the Company issued a press release, a copy of which is attached as Exhibit 99.1 to this Current Report on Form 8-K, announcing the pricing of the IPO. On January 28, 2026, the Company issued a press release, a copy of which is attached as Exhibit 99.2 to this Current Report on Form 8-K, announcing the closing of the IPO.