Company: RCUS
Filing Date: 2025-10-31
Form Type: 424B5
Source: 0001193125-25-260836
Chunk: 0

Company: Arcus Biosciences, Inc.
Filing Date: 2025-10-31
Form: 424B5
Chunk 0
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Filed Pursuant to Rule 424(b)(5)
Registration No. 333-270132 PROSPECTUS SUPPLEMENT (To Prospectus dated February 28, 2023) 13,700,000 Shares Common Stock We are offering 13,700,000 shares of our common stock. Our common stock is listed on the New York Stock Exchange under the symbol “RCUS.” On October 30, 2025, the last reported sale price of our common stock was $20.19 per share. Investing in our common stock involves risk. See the section titled “ Risk Factors” beginning on page S-9 of this prospectus supplement. Neither the U.S. Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus supplement or the accompanying prospectus. Any representation to the contrary is a criminal offense.

|                                           |     | Per   
 Share |        |     | Total |             |
|:------------------------------------------|:----|:------|-------:|:----|:------|------------:|
| Public offering price                     |     | $     | 18.250 |     | $     | 250,025,000 |
| Underwriting discounts and commissions(1) |     | $     |  1.095 |     | $     |  15,001,500 |
| Proceeds to us, before expenses           |     | $     | 17.155 |     | $     | 235,023,500 |

| (1) | See “Underwriting” for additional information regarding underwriting compensation. |

We have granted the underwriters an option for a period of 30 days from the date of this prospectus supplement to purchase up to an additional 2,055,000 shares of common stock. The underwriters expect to deliver the shares of common stock to purchasers against payment on or about November 3, 2025.

| Leerink Partners |     | Goldman Sachs & Co. LLC |     | Cantor |     | Mizuho |     | Truist Securities |

Prospectus Supplement dated October 30, 2025

TABLE OF CONTENTS PROSPECTUS SUPPLEMENT

|                                                                      |     | Page |      |
| ABOUT THIS PROSPECTUS SUPPLEMENT                                     |     |      | S-ii |
| PROSPECTUS SUPPLEMENT SUMMARY                                        |     |      | S-1  |
| RISK FACTORS