Exhibit 3.1

CERTIFICATE OF AMENDMENT

TO

FOURTH AMENDED AND RESTATED CERTIFICATE OF INCORPORATION

OF

RAYZEBIO, INC.

RayzeBio, Inc. (the “Corporation”), a corporation organized and existing under and by virtue of the General Corporation Law of the State of Delaware (the “DGCL”), does hereby certify that:

FIRST: The name of the Corporation is RayzeBio, Inc. The Certificate of Incorporation of the Corporation was originally filed with the Secretary of State of the State of Delaware on January 2, 2020 under the name of the Corporation (the “Certificate of Incorporation”).

SECOND: That the Board of Directors of the Corporation duly adopted resolutions approving the following amendment of the Fourth Amended and Restated Certificate of Incorporation, declaring said amendment to be advisable and in the best interests of the Corporation and its stockholders, and authorizing the appropriate officers of the Corporation to solicit the consent of the stockholders therefor.

THIRD: The following is hereby inserted into Article FOURTH of the Fourth Amended and Restated Certificate of Incorporation immediately before the first sentence therein:

Effective upon the filing of this Certificate of Amendment of the Amended and Restated Certificate of Incorporation with the Secretary of State of the State of Delaware (the “Effective Time”), every 5.141 shares of Common Stock or Preferred Stock then issued and outstanding or held in the treasury of the Corporation immediately prior to the Effective Time shall automatically be combined into one (1) share of Common Stock or Preferred Stock, as applicable, without any further action by the holders of such shares (the “Reverse Stock Split”). The Reverse Stock Split will be effected on a certificate-by-certificate basis, and any fractional shares resulting from such combination shall be rounded down to the nearest whole share on a certificate-by-certificate basis. No fractional shares shall be issued in connection with the Reverse Stock Split. In lieu of any fractional shares to which a holder would otherwise be entitled, the Corporation shall pay cash equal to such fraction multiplied by the fair market value of a share of Common Stock as determined in good faith by the Corporation’s Board of Directors. The Reverse Stock Split shall occur automatically without any further action by the holders of the shares of Common Stock and Preferred Stock affected thereby. All rights, preferences and privileges of the Common Stock and the Preferred Stock shall be appropriately adjusted to reflect the Reverse Stock Split in accordance with this Fourth Amended and Restated Certificate of Incorporation.

FOURTH: The foregoing amendment was approved by the holders of the requisite number of shares of the Corporation in accordance with Section 228 of the General Corporation Law.

FIFTH: The foregoing amendment to the Fourth Amended and Restated Certificate of Incorporation was duly adopted in accordance with the provisions of Section 242 of the DGCL.

FOURTH: This Certificate of Amendment, and the amendment to the Fourth Amended and Restated Certificate of Incorporation contained herein, shall be effective at 4:00 pm, Pacific Time, on September 7, 2023.

[SIGNATURE PAGE FOLLOWS]

IN WITNESS WHEREOF, the undersigned has caused this Certificate of Amendment to be signed by its duly authorized officer on the 7th day of September, 2023.

RayzeBio, Inc.
By:	/s/ Ken Song
Name:	Ken Song, M.D.
Title:	Chief Executive Officer