Company: RCUS
Filing Date: 2025-10-31
Form Type: 424B5
Source: 0001193125-25-260836
Chunk: 9

Company: Arcus Biosciences, Inc.
Filing Date: 2025-10-31
Form: 424B5
Chunk 9
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 and potentially expose us to notification obligations, loss, liability or reputational damage and otherwise adversely affect our business.                  |

| • |     | Failure to comply with privacy and data protection laws, regulations or other obligations could lead to                                                                                        
 government enforcement actions (which could include civil or criminal penalties), private litigation, and/or adverse publicity and could negatively affect our operating results and business. |

S-5

Corporate Information

We were incorporated in Delaware on April 30, 2015. Our principal executive offices are located at 3928 Point Eden Way, Hayward, CA 94545, and our
telephone number is (510) 694-6200. Our website address is www.arcusbio.com. The information on, or that can be accessed through, our website is not part of this prospectus. We have included our website
address as an inactive textual reference only.

Arcus Biosciences and the Arcus Biosciences logo are the property of Arcus. Trade names, trademarks and
service marks of other companies appearing in this prospectus are the property of their respective holders.

S-6

The Offering

| Common stock offered by us | 13,700,000 shares |

| Underwriters’ option to purchase additional 
 shares of common stock                      | We have granted the underwriters a 30-day option to purchase up to 2,055,000 additional shares of our common stock at the public offering price, less underwriting discounts and commissions. |

| Common stock to be outstanding immediately after 
 this offering                                    | 120,801,086 shares of common stock (122,856,086 shares if the underwriters exercise their option to purchase additional shares of our common stock in full). |

| Use of proceeds | We estimate that the net proceeds to us from this offering, after deducting underwriting discounts and commissions and estimated offering expenses payable by us, will be approximately $234.5 million, or approximately $269.7 million if the            
 underwriters exercise their option to purchase additional shares of our common stock in full. We currently intend to use the net proceeds from this offering to fund ongoing research and development activities, including the expansion of our clinical 
 development program for casdatifan and the discovery and clinical development of investigational candidates from our immunology and inflammation portfolio and other general corporate purposes, including working capital and operating expenses. See    
 “Use of Proceeds” on page S-12 of this prospectus supplement.                                                                                                                                                                                             |

| New York Stock Exchange trading symbol |