GigCapital8 Corp.

Item 8.01 Other Events. On June 25, 2026, GigCapital8 Corp. (the “Company” or “GigCapital8”), WISeKey International Holding Ltd. (“WISeKey”), a global leader in cybersecurity and trusted digital ecosystems, and its subsidiary SEALSQ Corp. (Nasdaq LAES), issued a joint press release, which is attached as Exhibit 99.1 hereto, announcing that the WISeKey and SEALSQ jointly established special purpose vehicle, Quantisimo Corp. (“Quantisimo”), and the Company have entered into a non-binding letter of intent (the “Letter of Intent”) for a business combination. Quantisimo was created by WISeKey and SEALSQ to establish a Trusted Quantum Pure-Play platform designed to provide investors with direct exposure to the rapidly emerging quantum economy. Through a combination of proprietary technologies, strategic investments, intellectual property, and selected assets from the SealQuantum.com portfolio of companies, Quantisimo seeks to become a leading public company focused on the development, commercialization, and deployment of trusted quantum technologies. Under the terms of the Letter of Intent, the Company and Quantisimo intend to enter into a definitive agreement pursuant to which the Company and Quantisimo would combine, with the former equityholders of both entities holding equity in the combined public company listed on a national stock exchange (the “Surviving Company”) and with Quatisimo’s existing equityholders owning a majority of the equity in the Surviving Company. The final terms of the definitive agreement are subject to the completion of due diligence to the Company’s satisfaction. Under the terms of the Letter of Intent, the pre-money enterprise value of Quantisimo is approximately $575 million. It is expected that there will be a substantial rollover of equity by the existing equityholders of Quantisimo. The completion of the business combination is subject to the negotiation and execution of definitive documentation and satisfaction of customary closing conditions stated in the Letter of Intent, including (i) completion of any required stock exchange and regulatory review, (ii) approval of the transaction by the Company’s shareholders, and (iii) financing arrangements being secured. Accordingly, no assurances can be made that the parties will successfully negotiate and enter into a definitive agreement, or that the proposed transaction will be consummated on the terms or timeframe currently contemplated, or at all. Additional Information and Where to Find It If a definitive agreement is entered into in connection with the proposed business combination, GigCapital8 and Quantisimo will prepare a proxy statement/prospectus (the “GigCapital8 proxy statement/prospectus”) to be filed with the United States Securities and Exchange Commission (the “SEC”) and mailed to GigCapital8’s shareholders. GigCapital8 and Quantisimo urge investors and other interested persons to read, when available, the GigCapital8 proxy statement/prospectus, as well as other documents filed with the SEC, because these documents will contain important information about the proposed business combination. Such persons can also read GigCapital8’s Annual Report on Form 10-K for the fiscal year ended December 31, 2025 (the “GigCapital8 Annual Report”), for a description of the security holdings of its officers and directors and their respective interests as security holders in the consummation of the transactions described herein. The GigCapital8 proxy statement statement/prospectus, once available, and GigCapital8 Annual Report can be obtained, without charge, at the SEC’s web site (http://www.sec.gov). Participants in the Solicitation GigCapital8, WISeKey, SEALSQ, Quantisimo, and their respective directors, executive officers, and certain other members of management and employees may be deemed participants in any solicitation of proxies from GigCapital8 shareholders in connection with the proposed transaction. Information regarding GigCapital8’s directors and executive officers is contained in GigCapital8’s filings with the SEC. Additional information regarding the interests of such participants in the proposed transaction, which may, in some cases, be different than those of GigCapital8’s and Quantisimo’s Equityholders generally, will be included in any proxy statement, registration statement, prospectus, or other relevant documents filed with the SEC if and when such documents become available.