Company: RCUS
Filing Date: 2025-10-31
Form Type: 424B5
Source: 0001193125-25-260836
Chunk: 11

Company: Arcus Biosciences, Inc.
Filing Date: 2025-10-31
Form: 424B5
Chunk 11
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 reflects and assumes the following:

| • |     | no exercise of the underwriters’ option to purchase additional shares of common stock. |

S-8

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, 2025, 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, we may
invest the net proceeds from this offering in a manner that does not produce income or that loses value. Our failure to apply these funds effectively could have a material adverse effect on our business and cause the price of our common stock to
decline.

If you purchase shares of common stock in this offering, you will experience immediate dilution in your investment.

Purchasers of common stock in this offering will pay a price per share in this offering that exceeds the net tangible book value per share of our common stock.
Assuming that an aggregate of 13,700,000 shares of common stock are sold at a public offering price of $18.25 per share, for aggregate net proceeds of approximately $234.5 million and after deducting underwriting discounts and commissions and
estimated offering expenses payable by us, if you purchase shares of our common stock in this offering, you will experience immediate dilution of $12.70 per share (or $12.51 per