Keystone Acquisition Corp.

Item 8.01. Other Events. As previously reported, on June 4, 2026, Keystone Acquisition Corp. (the “Company”) consummated its initial public offering (“IPO”) of 28,750,000 units (the “Units”), including the issuance of 3,750,000 Units as a result of the underwriters’ exercise of their over-allotment option in full. Each Unit consists of one Class A ordinary share of the Company, par value $0.0001 per share (the “Class A Ordinary Shares”), and one-half of one redeemable warrant of the Company (each whole warrant, a “Warrant”), with each Warrant entitling the holder thereof to purchase one Class A Ordinary Share for $11.50 per share, subject to adjustment. The Units were sold at a price of $10.00 per Unit, generating gross proceeds to the Company of $287,500,000. Also as previously reported, on June 4, 2026, simultaneously with the consummation of the IPO, the Company completed the private sale (the “Private Placement”) of an aggregate of 8,468,750 warrants (the “Private Placement Warrants”) to Keystone International Acquisition Management LLC (the “Sponsor”), Cohen & Company Capital Markets, a division of Cohen & Company Securities, LLC and Clear Street LLC, as representatives of the underwriters (the “Representatives”) at a purchase price of $1.00 per Private Placement Warrant, generating gross proceeds to the Company of $8,468,750. Of the 8,468,750 Private Placement Warrants, the Sponsor purchased 5,593,750 Private Placement Warrants and the Representatives purchased 2,875,000 Private Placement Warrants. A total of $288,218,750 of the proceeds from the IPO and Private Placement, which amount includes up to $11,500,000 of the underwriters’ deferred commission, was placed in a U.S.-based trust account maintained by Efficiency INC., acting as trustee. An audited balance sheet as of June 4, 2026 reflecting receipt of the proceeds upon consummation of the IPO and the Private Placement has been issued by the Company and is included as Exhibit 99.1 to this Current Report on Form 8-K.