Company: RCUS
Filing Date: 2025-02-18
Form Type: 424B5
Source: 0001193125-25-028669
Chunk: 10

Company: Arcus Biosciences, Inc.
Filing Date: 2025-02-18
Form: 424B5
Chunk 10
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”), as of September 30, 2024;                                          |

| • |     | up to an aggregate of 2,902,327 shares of common stock reserved for issuance under our 2018 Employee Stock                                                                                                     
 Purchase Plan (our “Purchase Plan”), as of September 30, 2024, as well as any annual automatic increases in the number of shares of our common stock reserved for future issuance under the Purchase Plan; and |

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| • |     | any of the shares of our common stock that may be issued and sold to Gilead pursuant to the Third Amended and                                                                                         
 Restated Common Stock Purchase Agreement, dated January 29, 2024 between us and Gilead (the “Stock Purchase Agreement”), which, as of September 30, 2024, was up to an aggregate of 3,020,000 shares. |

In addition, unless we specifically state otherwise, all information in this prospectus supplement reflects and assumes no exercise of outstanding stock options or vesting and settlement of restricted stock units after September 30, 2024.

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RISK FACTORS

Investing in our common stock involves a high degree of risk. You should carefully consider the risk factors described below and the risk factors incorporated by reference from our Quarterly Report on Form 10-Qfor the three months ended September 30, 2024, and all other information contained or incorporated by reference in this prospectus supplement and the accompanying prospectus, including our financial statements and the related notes, as may be updated by our subsequent filings under the Securities Exchange Act of 1934, as amended (“Exchange Act”) and in any free writing prospectus that we have authorized for use in connection with this offering before acquiring shares of our common stock. These risks could have a material and adverse impact on our business, results of operations, financial condition and growth prospects, which may cause the trading price of our common stock to decline and you could lose all or part of your investment.

Risks related to this offering

Management will have broad discretion as to the use of the proceeds from this offering, and we may not use the proceeds effectively.

Our management will have broad discretion in the application of the net proceeds from this offering, and could spend the proceeds in
ways that do not improve our results of operations or enhance the value of our common stock. In addition, we may choose to accelerate or deaccelerate our spending depending on results from clinical trials and other factors. Pending their use,