Exhibit 3.1

AMENDED AND RESTATED

CERTIFICATE OF INCORPORATION

OF

ACELYRIN, INC.

SECTION 1.

The name of this corporation is ACELYRIN, Inc. (the “Corporation”).

SECTION 2.

The address of the registered office of the Corporation in the State of Delaware shall be 3500 S. Dupont Highway, Dover, County of Kent, Delaware 19901, or in such other location as the board of directors of the Corporation (the “Board of Directors”) may from time to time determine or the business of the Corporation may require. The Corporation’s registered agent for service of process at such address is Incorporating Services, Ltd.

SECTION 3.

The purpose of the Corporation is to engage in any lawful act or activity for which a corporation may be organized under the Delaware General Corporation Law (“DGCL”).

SECTION 4.

The Corporation is authorized to issue only one class of stock, to be designated as common stock of the Corporation (the “Common Stock”). The total number of shares of Common Stock presently authorized is 1,000, each having a par value of $0.00001.

SECTION 5.

For the management of the business and for the conduct of the affairs of the Corporation, and in further definition, limitation and regulation of the powers of the Corporation, of its directors and stockholders, or any class or series thereof, as the case may be, it is further provided that:

Section 5.1 MANAGEMENT OF THE BUSINESS.

Except as otherwise provided by the DGCL or this certificate of incorporation (as amended and/or restated from time to time, the “Certificate of Incorporation”) with the Secretary of State of the State of Delaware, the business and affairs of the Corporation shall be managed by or under the direction of the Board of Directors of the Corporation (the “Board”). Subject to any rights of the holders of shares of any one or more series of Preferred Stock then outstanding to elect additional directors under specified circumstances, the number of directors that shall constitute the Board shall be fixed exclusively by the Board.

Section 5.2 BOARD OF DIRECTORS

Subject to the rights of the holders of any one or more series of Preferred Stock to elect additional directors under specified circumstances, the directors shall be divided into three classes designated as Class I, Class II and Class III, respectively. The Board is authorized to assign members of the Board already in office to such classes at the time the classification becomes effective. At the first annual

meeting of stockholders following the time at which the initial classification of the Board becomes effective, the initial term of office of the Class I directors shall expire and Class I directors shall be elected for a full term of three years. At the second annual meeting of stockholders following the time at which the initial classification of the Board becomes effective, the initial term of office of the Class II directors shall expire and Class II directors shall be elected for a full term of three years. At the third annual meeting of stockholders following the time at which the initial classification of the Board becomes effective, the initial term of office of the Class III directors shall expire and Class III directors shall be elected for a full term of three years. At each succeeding annual meeting of stockholders, directors shall be elected for a full term of three years ending on the date of the third annual meeting of stockholders following the annual meeting of stockholders at which such director was elected to succeed the directors of the class whose terms expire at such annual meeting.

Section 5.3 REMOVAL OF DIRECTORS

Subject to the rights of the holders of any one or more series of Preferred Stock to remove directors elected by such series of Preferred Stock, any individual director or the entire Board may be removed from office at any time, but only for cause, and only by the affirmative vote of the holders of 66-2/3% of the voting power of all the then-outstanding shares of the capital stock of the Corporation entitled to vote generally at an election of directors, voting together as a single class.

Section 5.4 VACANCIES AND NEWLY CREATED DIRECTORSHIPS.

Subject to any limitations imposed by applicable law and subject to the rights of the holders of any one or more series of Preferred Stock to elect additional directors under specified circumstances or fill vacancies in respect of such directors, any vacancies on the Board resulting from death, resignation, disqualification, removal or other causes and any newly created directorships resulting from any increase in the number of directors, shall be filled only by the affirmative vote of a majority of the directors then in office, even though less than a quorum of the Board, or by a sole remaining director, and not by the stockholders. Any director elected to fill a newly created directorship or vacancy in accordance with the preceding sentence shall hold office until the next annual meeting of stockholders held to elect the class of directors to which such director is elected and until such director’s successor shall have been elected and qualified or such director’s earlier death, resignation or removal.

Section 5.5 PREFERRED STOCKHOLDERS ELECTION RIGHTS.

Whenever the holders of any one or more series of Preferred Stock shall have the right, voting separately as a series or separately as a class with one or more such other series, to elect directors at an annual or special meeting of stockholders, the election, term of office, removal and other features of such directorships shall be governed by the terms of the Certificate of Incorporation (including any certificate of designation relating to any series of Preferred Stock) applicable thereto. The number of directors that may be elected by the holders of any such series of Preferred Stock shall be in addition to the number fixed pursuant to Section 5.1 hereof, and the total number of directors constituting the whole Board shall be automatically adjusted accordingly. Except as otherwise provided by the Board in the resolution or resolutions establishing such series, whenever the holders of any series of Preferred Stock having such right to elect additional directors are divested of such right pursuant to the provisions of such stock, the terms of office of all such additional directors elected by the holders of such stock, or elected to fill any vacancies resulting from the death, resignation, disqualification or removal of such additional directors, shall forthwith terminate (in which case each such director thereupon shall cease to be qualified as, and shall cease to be, a director) and the total authorized number of directors of the Corporation shall automatically be reduced accordingly.

Section 5.6 BYLAW AMENDMENTS.

The Board is expressly authorized and empowered to adopt, amend or repeal any provisions of the bylaws of the Corporation (as amended and/or restated, from time to time, the “Bylaws”) without the assent or vote of the stockholders. The stockholders shall also have power to adopt, amend or repeal the Bylaws; provided, however, that, in addition to any vote of the holders of any class or series of stock of the Corporation required by applicable law or by the Certificate of Incorporation, such action by stockholders shall require the affirmative vote of the holders of at least 66-2/3% of the voting power of all of the then-outstanding shares of the capital stock of the Corporation entitled to vote thereon, voting together as a single class.

Section 5.7 STOCKHOLDER ACTIONS.

a. The directors of the Corporation need not be elected by written ballot unless the Bylaws so provide.

b. Subject to any rights of the holders of shares of any one or more series of Preferred Stock then outstanding, any action required or permitted to be taken by the stockholders of the Corporation must be effected at an annual or special meeting of the stockholders and may not be effected by consent in lieu of a meeting.

c. Subject to any rights of the holders of shares of any series of Preferred Stock then outstanding, special meetings of stockholders of the Corporation may be called only by the Chairperson of the Board, the Chief Executive Officer, or the Board, and a special meeting may not be called by any other person or persons and any power of stockholders to call a special meeting of stockholders is specifically denied. Only such business shall be considered at a special meeting of stockholders as shall have been stated in the notice for such meeting.

d. Advance notice of stockholder nominations for election of directors and other business to be brought by stockholders before a meeting of stockholders shall be given in the manner provided by the Bylaws.

e. An annual meeting of stockholders for the purpose of election of directors and for such other business as may properly come before the meeting, shall be held on such date, time and place, if any, as may be determined from time to time by the Board.

SECTION 6.

No director or officer of the Corporation shall be liable to the Corporation or its stockholders for monetary damages for breach of fiduciary duty as a director or officer, except to the extent such exemption from liability or limitation thereof is not permitted under the DGCL, as the same exists or may hereafter be amended. To the fullest extent permitted by applicable law, the Corporation is authorized to provide indemnification of (and advancement of expenses to) directors, officers, employees and other agents of the Corporation (and any other persons to which applicable law permits the Company to provide indemnification) through provisions in the Bylaws, agreements with such agents or other persons, vote of stockholders or disinterested directors or otherwise in excess of the indemnification and advancement otherwise permitted by such applicable law. If applicable law is amended after approval by the stockholders of this Section 6 to authorize corporate action further eliminating or limiting the personal liability of directors or officers, then the liability of a director or officer to the Company shall be eliminated or limited to the fullest extent permitted by applicable law as so amended. Any amendment, modification or repeal of this Section 6 shall not adversely affect any right or protection of a director or

officer of the Corporation hereunder in respect of any act or omission occurring prior to the time of such amendment, modification or repeal.

SECTION 7.

Section 7.1 Unless the Corporation consents in writing to the selection of an alternative forum, the Court of Chancery of the State of Delaware (or, if and only if the Court of Chancery of the State of Delaware lacks subject matter jurisdiction, any state court located within the State of Delaware or, if and only if all such state courts lack subject matter jurisdiction, the federal district court for the District of Delaware) and any appellate court therefrom shall be the sole and exclusive forum for the following claims or causes of action under Delaware statutory or common law: (A) any derivative claim or cause of action brought on behalf of the Corporation; (B) any claim or cause of action for breach of a fiduciary duty owed by any current or former director, officer or other employee or stockholder of the Corporation, to the Corporation or the Corporation’s stockholders; (C) any claim or cause of action against the Corporation or any current or former director, officer or other employee of the Corporation, arising out of or pursuant to any provision of the DGCL, the Certificate of Incorporation or the Bylaws; (D) any claim or cause of action seeking to interpret, apply, enforce or determine the validity of the Certificate of Incorporation or the Bylaws (including any right, obligation, or remedy thereunder); (E) any claim or cause of action as to which the DGCL confers jurisdiction on the Court of Chancery of the State of Delaware; and (F) any claim or cause of action against the Corporation or any current or former director, officer or other employee of the Corporation, governed by the internal-affairs doctrine or otherwise related to the Corporation’s internal affairs, in all cases to the fullest extent permitted by applicable law and subject to the court having personal jurisdiction over the indispensable parties named as defendants. This Section 7.1 shall not apply to claims or causes of action brought to enforce a duty or liability created by the Securities Act of 1933, as amended (the “1933 Act”), or the Securities Exchange Act of 1934, as amended, or any other claim for which the federal courts have exclusive jurisdiction.

Section 7.2 Unless the Corporation consents in writing to the selection of an alternative forum, to the fullest extent permitted by applicable law, the federal district courts of the United States of America shall be the exclusive forum for the resolution of any complaint asserting a cause of action arising under the 1933 Act, including all causes of action asserted against any defendant named in such complaint. For the avoidance of doubt, this provision is intended to benefit and may be enforced by the Corporation, its officers and directors, the underwriters for any offering giving rise to such complaint, and any other professional entity whose profession gives authority to a statement made by that person or entity and who has prepared or certified any part of the documents underlying the offering.

SECTION 8.

Section 8.1 Any person or entity holding, owning, or otherwise acquiring any interest in any security of the Corporation shall be deemed to have notice of and consented to the provisions of the Certificate of Incorporation.

Section 8.2 The Corporation reserves the right to amend, alter, change or repeal, at any time and from time to time, any provision contained in the Certificate of Incorporation, in the manner now or hereafter prescribed by statute, except as provided in Section 8.3, and all rights, preferences and privileges of whatsoever nature conferred upon the stockholders, directors or any other persons whomsoever by and pursuant to the Certificate of Incorporation are granted subject to this reservation.

Section 8.3 Notwithstanding any other provisions of the Certificate of Incorporation or any provision of applicable law that might otherwise permit a lesser vote or no vote, but in addition to any affirmative vote of the holders of any particular class or series of capital stock of the Corporation required by applicable law or by the Certificate of Incorporation or any certificate of designation filed with respect to a series of

Preferred Stock, the affirmative vote of the holders of at least 66²/₃% of the voting power of all of the then-outstanding shares of capital stock of the Corporation entitled to vote thereon, voting together as a single class, shall be required to alter, amend or repeal (whether by merger, consolidation, conversion or otherwise), or adopt any provision inconsistent with, Sections 5, 6, 7 and this Section 8.

SECTION 9.

Section 9.1 If any provision or provisions of the Certificate of Incorporation shall be held to be invalid, illegal or unenforceable as applied to any circumstance for any reason whatsoever, the validity, legality and enforceability of such provisions in any other circumstance and of the remaining provisions of the Certificate of Incorporation (including, without limitation, each portion of any paragraph of the Certificate of Incorporation containing any such provision held to be invalid, illegal or unenforceable that is not itself held to be invalid, illegal or unenforceable) shall not, to the fullest extent permitted by applicable law, in any way be affected or impaired thereby.

Section 9.2 Notwithstanding anything to the contrary herein, in the event that there is no authorized class of “Preferred Stock” all references to “Preferred Stock” in this Certificate of Incorporation shall mean “Common Stock”.