Summit Therapeutics Inc.

Item 1.01 Entry into a Material Definitive Agreement. On July 23, 2026, Summit Therapeutics Inc. (the “Company”) entered into a distribution agreement (the “Distribution Agreement”) with J.P. Morgan Securities LLC (“Sales Agent”), as sales agent, pursuant to which the Company may offer and sell, from time to time, through the Sales Agent, shares of the Company’s common stock, par value $0.01 per share, having an aggregate offering price of up to $380,000,000 (the “Shares”). The Company is not obligated to sell any Shares under the Distribution Agreement. Subject to the terms and conditions of the Distribution Agreement, the Sales Agent will use commercially reasonable efforts, consistent with its normal trading and sales practices, to sell Shares from time to time based upon the Company’s instructions, including any price, time or size limits or other customary parameters or conditions specified by the Company. Under the Distribution Agreement, the Sales Agent may sell Shares in transactions that are deemed to be “at the market” offerings as defined in Rule 415(a)(4) under the Securities Act of 1933, as amended, including sales made by means of ordinary brokers’ transactions, including directly on the Nasdaq Global Market or into any other existing trading market for the Shares, or sales made to or through a market maker, in block transactions or by any other method permitted by law, including negotiated transactions. Sales may be made at market prices prevailing at the time of a sale or at prices related to prevailing market prices or at negotiated prices. The Company will pay the Sales Agent a commission of up to 3.0% of the gross sales price per share sold through it acting as Sales Agent. The Company has no obligation to sell any of the Shares under the Distribution Agreement and may at any time suspend solicitations and offers under the Distribution Agreement. The issuance and sale, if any, of the Shares by the Company under the Distribution Agreement will be made pursuant to the Company’s effective registration statement on Form S-3 (File No. 333-296642) filed with the U.S. Securities and Exchange Commission (the “SEC”) on June 9, 2026, and which became automatically effective upon filing. The Company filed a prospectus supplement with the SEC on July 23, 2026 in connection with the offer and sale of the Shares pursuant to the Distribution Agreement. The foregoing description of the Distribution Agreement does not purport to be complete and is qualified in its entirety by reference to the full text of the Distribution Agreement, a copy of which is filed as Exhibit 1.1 to this Current Report on Form 8-K and is incorporated herein by reference. The legal opinion of Baker & Hostetler LLP, counsel to the Company, relating to the validity of the issuance and sale of the Shares being offered pursuant to the Distribution Agreement, is filed as Exhibit 5.1 to this Current Report on Form 8-K and is incorporated herein by reference. This Current Report on Form 8-K shall not constitute an offer to sell or the solicitation of an offer to buy any Shares under the Distribution Agreement nor shall there be any sale of such Shares in any state in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state.