Aptevo Therapeutics Inc.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, DC 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934

(Amendment No.__)

Check the appropriate box:

Aptevo Therapeutics Inc.

(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement if Other Than the Registrant)

Payment of Filing Fee (Check all boxes that apply)

Seattle, Washington 98121

NOTICE OF SPECIAL MEETING OF STOCKHOLDERS

To Be Held on September 22, 2026

Dear Aptevo Stockholder:

You are cordially invited to virtually attend a special meeting of the stockholders (the “Special Meeting”) of Aptevo Therapeutics Inc., a Delaware corporation (“Aptevo,” “we,” “us,” “our,” or the “Company”). The meeting will be held on September 22, 2026, at 10 a.m. Pacific Time. To facilitate stockholder participation and save costs, the Special Meeting will be held in a virtual meeting format only at www.virtualshareholdermeeting.com/APVO2026SM2. The meeting will be held for the following purposes:

1. To approve an amendment and restatement of our Restated Certificate of Incorporation, as amended (the “Certificate of Incorporation”), to include previous amendments to the Certificate of Incorporation and the designation of Series A Junior Participating Preferred Stock (the “Series A Preferred Stock”) and to make certain other technical and administrative changes (“Proposal 1” or the “A&R Certificate of Incorporation Proposal”);

2. To approve, in accordance with Nasdaq Listing Rule 5635(d), the issuance of shares of the Company’s Common Stock, par value $0.001 per share (“Common Stock”), and/or securities convertible into or exercisable for Common Stock, that equals 20% or more of the Common Stock or 20% or more of the voting power outstanding before the issuance, including Common Stock (i) issuable upon the exercise of the common stock purchase warrants (the “Inducement Warrants”), issued and sold in a private placement pursuant to Warrant Inducement and Reload Letters, dated as of August 12, 2026, by and among the Company and the holder parties thereto (the “Inducement Letters”), and (ii) issuable upon the exercise of the common stock purchase warrants (the “Common Warrants”) that were issued and sold in private placement transactions pursuant to that certain Securities Purchase Agreement (the “Purchase Agreement”), dated as of August 12, 2026, by and among the Company and the purchaser parties thereto (“Proposal 2” or the “Stock and Warrant Issuance Proposal”);

3. To approve the Aptevo Therapeutics Inc. Fifth Amended and Restated 2018 Stock Incentive Plan (“Proposal 3” or the “Stock Incentive Plan Proposal”); and

4. To authorize an adjournment of the meeting to a later date or dates, if necessary or appropriate, to solicit additional proxies if there are not sufficient votes in favor of Proposal 1, Proposal 2 or Proposal 3 (“Proposal 4” or the “Adjournment Proposal”).

These items of business are more fully described in the proxy statement (the “Proxy Statement”) accompanying this Notice (“Notice”).

In addition to the foregoing, the Special Meeting will include the transaction of any other business relating to the purpose or purposes stated in this Notice and the accompanying Proxy Statement that may be properly brought before the meeting or any continuation, adjournment or postponement thereof.

The record date for the Special Meeting is August 13, 2026. Only stockholders of record at the close of business on that date may vote on the proposals being presented at the Special Meeting or any adjournment, postponement, rescheduling, or continuation thereof.

Important Notice Regarding the Availability of Proxy Materials for the Special Meeting to Be Held Virtually on September 22, 2026 at 10 a.m. Pacific Time at www.virtualshareholdermeeting.com/APVO2026SM2.

The Proxy Statement is available at www.proxyvote.com.

By Order of the Board of Directors

/s/ SoYoung Kwon

SVP, General Counsel, Business Development and Corporate Affairs

Seattle, WA

August 31, 2026

Whether or not you expect to attend the Special Meeting, please complete, date, sign and return the enclosed proxy, or vote over the telephone or the Internet as instructed in these materials, as promptly as possible in order to ensure your representation at the meeting. Even if you have voted by proxy, you may still vote if you attend the virtual meeting. Please note, however, that if your shares are held of record by a broker, bank or other nominee and you wish to vote at the virtual meeting, you must obtain a proxy issued in your name from that record holder.

TABLE OF CONTENTS

Seattle, Washington 98121

PROXY STATEMENT

FOR THE SPECIAL MEETING OF STOCKHOLDERS

To be held on September 22, 2026