of this Form 8-K (including Exhibit 99.1) is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended or the Exchange Act, except as expressly set forth by specific reference in such filing.

of this Form 8-K (including Exhibit 99.1) is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended or the Exchange Act, except as expressly set forth by specific reference in such filing.

Other Events. STAR-121 Update . On April 20, 2026, Arcus Biosciences, Inc. (the “ Company ”) announced the discontinuation of the Phase 3 STAR-121 study, which is being conducted in collaboration with Gilead Sciences, Inc. (“ Gilead ”), due to futility. STAR-121 evaluated the anti-TIGIT antibody domvanalimab plus anti-PD-1 antibody zimberelimab and chemotherapy versus pembrolizumab plus chemotherapy as a first-line treatment for metastatic non-small cell lung cancer. The decision is based on…

Chief Operating Officer — Jennifer Jarrett: Jennifer Jarrett resigned from her position as Chief Operating Officer.

of this Form 8-K (including Exhibit 99.1) is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended or the Exchange Act, except as expressly set forth by specific reference in such filing.

by reference. SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized. ARCUS BIOSCIENCES, INC. Date: December 18, 2025 By: /s/ Terry Rosen, Ph. D. Terry Rosen, Ph.D. Chief Executive Officer (Principal Executive Officer)

Entry into a Material Definitive Agreement. On December 18, 2025 (the “Closing Date”), Arcus Biosciences, Inc. (the “Company”) entered into a First Amendment to the Loan and Security Agreement (the “First Amendment”) with the several banks and other financial institutions or entities party thereto (the “Lenders”), as lenders, and Hercules Capital, Inc. (“Hercules”), as administrative agent and collateral agent. The First Amendment amended the terms of that certain Loan and Security Agreement,…

Other Events. On December 12, 2025, Arcus Biosciences, Inc. (the “Company”) announced the discontinuation of the Phase 3 STAR-221 study due to futility. STAR-221 evaluated the anti-TIGIT antibody domvanalimab plus anti-PD-1 antibody zimberelimab and chemotherapy versus nivolumab plus chemotherapy as a first-line treatment for advanced gastric and esophageal cancers. The decision is based on the recommendation from the Independent Data Monitoring Committee following its review of data from an…

Other Events. On October 30, 2025, Arcus Biosciences, Inc. (the “ Company ”) entered into an underwriting agreement (the “ Underwriting Agreement ”) with Leerink Partners LLC and Goldman Sachs & Co. LLC, as representatives of the several underwriters named therein (collectively, the “ Underwriters ”), relating to the public offering, issuance and sale of 13,700,000 shares of the Company’s common stock (“ Common Stock ”), at the public offering price of $18.25 per share (the “Offering”). Under…

of this Form 8-K (including Exhibit 99.1) is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended or the Exchange Act, except as expressly set forth by specific reference in such filing.

Other Events. ARC-20 Updates On October 6, 2025, Arcus Biosciences, Inc. (the “Company”) presented updated data from the monotherapy cohorts of ARC-20, a Phase 1/1b study evaluating different doses and combinations with casdatifan, and shared new research programs in immunology and inflammation. A copy of the presentation has been posted to the Investors & Media section of the Company’s website. The presentation included updated data from four monotherapy cohorts evaluating casdatifan in pati…

of this Form 8-K (including Exhibit 99.1) is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended or the Exchange Act, except as expressly set forth by specific reference in such filing.

of this Form 8-K (including Exhibit 99.1) is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended or the Exchange Act, except as expressly set forth by specific reference in such filing.

of this Form 8-K (including Exhibit 99.1) is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended or the Exchange Act, except as expressly set forth by specific reference in such filing.

Other Events. On February 18, 2025, Arcus Biosciences, Inc. (the “Company”) entered into an underwriting agreement (the “Underwriting Agreement”) with Goldman Sachs & Co. LLC and Leerink Partners LLC, as representatives of the several underwriters named therein (collectively, the “Underwriters”), in connection with the offering, issuance and sale by the Company of 13,636,364 shares of the Company’s common stock, $0.0001 par value per share (the “Common Stock”), at an offering price of $11.00…

Results of Operations and Financial Condition. On February 18, 2025, Arcus Biosciences, Inc. (the “Company”) reported that, as of December 31, 2024, it had approximately $992 million in cash, cash equivalents and marketable securities. This estimate of its cash, cash equivalents and marketable securities balance is preliminary and subject to completion of its financial closing procedures, including the completion of management’s reviews. Accordingly, the unaudited preliminary cash, cash equiv…

Director — Merdad Parsey, M.D., Ph.D.: The filing reports the routine replacement of a Gilead-designated board member with a new Gilead designee, which is a standard corporate governance update rather than a loss of senior executive management.

Chief Medical Officer — Dimitry Nuyten, M.D., Ph.D.: The departure of the Chief Medical Officer is accompanied by the immediate appointment of a successor, indicating an orderly succession rather than a sudden loss of leadership.

of this Form 8-K (including Exhibit 99.1) is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended or the Exchange Act, except as expressly set forth by specific reference in such filing.

Entry into a Material Definitive Agreement. On August 27, 2024 (the “ Closing Date ”), Arcus Biosciences, Inc. (the “ Company ”) entered into a Loan and Security Agreement (the “ LSA ”), by and among the Company, the several banks and other financial institutions or entities party thereto, as lenders, and Hercules Capital, Inc. (“ Hercules ”), as administrative agent and collateral agent. The LSA provides a secured term loan facility of up to $250.0 million (collectively, the “ Term Loans ”),…

by reference. SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized. ARCUS BIOSCIENCES, INC. Date: August 27, 2024 By: /s/ Terry Rosen, Ph. D. Terry Rosen, Ph.D. Chief Executive Officer (Principal Executive Officer)

of this Form 8-K (including Exhibit 99.1) is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended or the Exchange Act, except as expressly set forth by specific reference in such filing.

of this Form 8-K (including Exhibit 99.1) is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended or the Exchange Act, except as expressly set forth by specific reference in such filing.