ADTRAN Holdings, Inc.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

(Amendment No. )

Filed by the Registrant ☒

Filed by a party other than the Registrant ☐

Check the appropriate box:

ADTRAN Holdings, 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):

Notice of 2025

Annual Meeting and

Proxy Statement

March 31, 2025

Dear Stockholder:

You are cordially invited to attend the 2025 Annual Meeting of Stockholders of ADTRAN Holdings, Inc. to be held on Wednesday, May 14, 2025, at 10:30 a.m., Central Time. We are pleased to announce that this year’s Annual Meeting will be a virtual meeting conducted by live webcast on the Internet. You will be able to attend and participate in the meeting by visitingwww.virtualshareholdermeeting.com/ADTN2025 and entering the 16-digit control number included on your Notice of Internet Availability of Proxy Materials (the “Notice”) or on your proxy card if you receive the proxy materials by mail. You will not be able to attend the Annual Meeting in person.

The attached Notice of Annual Meeting of Stockholders and Proxy Statement describe the formal business to be transacted at the meeting. During the meeting, we also will report on Adtran’s operations during the past year and our plans for the future.

We have elected to take advantage of Securities and Exchange Commission rules that allow issuers to furnish proxy materials to their stockholders on the Internet. We believe that the rules will allow us to provide our stockholders with the information they need, while lowering the costs of delivery and reducing the environmental impact of the annual meeting.

Your vote, whether during the virtual meeting on May 14, 2025, or by proxy, is important. Please review the instructions on each of your voting options described in the accompanying proxy materials and the Notice you received in the mail. If you are unable to participate in the virtual meeting, I urge you to vote as soon as possible.

Sincerely,

THOMAS R. STANTON

Chairman of the Board

Notice of Annual Meeting of Stockholders

NOTICE HEREBY IS GIVEN that the 2025 Annual Meeting of Stockholders (the “Annual Meeting”) of ADTRAN Holdings, Inc. (the “Company”) will be held on Wednesday, May 14, 2025, at 10:30 a.m., Central Time, via live webcast. You can participate in the meeting by visiting www.virtualshareholdermeeting.com/ADTN2025 and entering the 16-digit control number included on your Notice or proxy card. If you hold your shares through an intermediary, such as a bank or broker, and do not have a control number, please contact the bank or broker. Please log in to the website by 10:15 a.m., Central Time, on the day of the meeting. There is no physical location for the Annual Meeting.

The Annual Meeting is being held for the purposes of considering and voting upon:

Stockholders will also consider and act upon such other business as may properly come before the Annual Meeting or any adjournments thereof. The Board of Directors is not aware of any other business to be presented for a vote of the stockholders at the Annual Meeting. See page 90 for additional details.

How to Vote

The Board of Directors recommends that you vote FOR each of the seven director nominees; FOR the approval on an advisory basis of the compensation of the Company’s NEOs; and FOR the ratification of the appointment of PricewaterhouseCoopers LLP as the Company’s independent registered public accounting firm for the fiscal year ending December 31, 2025. The Annual Meeting may be adjourned from time to time without notice other than announcement at the meeting or at adjournments thereof, and any business for which notice is hereby given may be transacted at any such adjournment.

Information relating to the above matters is set forth in the attached Proxy Statement. Stockholders of record at the close of business on March 17, 2025, are entitled to receive notice of and to vote during the Annual Meeting and any adjournments thereof.

Whether or not you plan to participate in the Annual Meeting, we urge you to review these materials carefully, which are available at https://materials.proxyvote.com/00486H. We also encourage you to vote by (i) following the instructions on the notice that you received from your broker, bank or other nominee if your shares are held beneficially in “street name” or (ii) one of the following means if your shares are registered directly in your name with the Company’s transfer agent:

By Internet: Go to the website www.proxyvote.com and follow the instructions. You will need the control number included on your Notice to obtain your records and vote by Internet.

By Telephone: From a touch-tone telephone, dial toll-free 1-800-690-6903 and follow the recorded instructions. You will need the control number included on your Notice in order to vote by telephone.

By Mail: You may request a hard copy of the proxy materials, including a proxy card, by following the instructions on your Notice. If you request and receive a proxy card, please mark your selections on the proxy card, date and sign your name exactly as it appears on the proxy card and mail the proxy card in the pre-paid envelope that will be provided to you. Mailed proxy cards must be received no later than May 13, 2025, in order to be counted for the Annual Meeting unless you are voting shares of common stock held in our 401(k) plan, in which case the deadline is May 12, 2025.

You can submit questions in advance of the Annual Meeting by visiting www.proxyvote.com, entering your 16-digit control number, and using the “Questions for Management” feature. You can submit questions during the Annual Meeting by following the instructions on the meeting website. Management will answer pertinent questions in the “Investor Resources” section of our website at https://investors.adtran.com. The questions and answers will be available as soon as practicable after the Annual Meeting and will remain available for thirty (30) days after posting.

By order of the Board of Directors,

Dana C. Crim

Senior Vice President, Administration and Corporate Secretary

Huntsville, Alabama

March 31, 2025

Table of Contents

Proxy Statement for the Annual

Meeting of Stockholders

To Be Held on Wednesday, May 14, 2025

This Proxy Statement, along with the accompanying Notice of Annual Meeting of Stockholders, contains information about the 2025 Annual Meeting of Stockholders (the “Annual Meeting”) of ADTRAN Holdings, Inc. (the “Company”), including any adjournments or postponements of the Annual Meeting. The Annual Meeting will be held on Wednesday, May 14, 2025, at 10:30 a.m., Central Time. We are pleased to announce that this year’s Annual Meeting will be a virtual meeting conducted by live webcast on the Internet. You will be able to attend and participate in the meeting by visitingwww.virtualshareholdermeeting.com/ADTN2025 and entering the 16-digit control number included on your Notice of Internet Availability of Proxy Materials (the “Notice”) or on your proxy card if you receive the proxy materials by mail. If you hold your shares through an intermediary, such as a bank or broker, and do not have a control number, please contact the bank or broker. Please log in to the website by 10:15 a.m., Central Time, on the day of the meeting. You may vote during the Annual Meeting by following the instructions available on the meeting website. There is no physical location for the Annual Meeting.

You can submit questions in advance of the Annual Meeting by visiting www.proxyvote.com, entering your 16-digit control number, and using the “Questions for Management” feature. You can submit questions during the Annual Meeting by following the instructions on the meeting website. Management will answer pertinent questions in the “Investor Resources” section of our website athttps://investors.adtran.com. The questions and answers will be available as soon as practicable after the Annual Meeting and will remain available for thirty (30) days after posting.

We are providing this Proxy Statement to the stockholders of the Company in connection with the solicitation of proxies by our Board of Directors to be voted during the Annual Meeting and at any adjournments of that meeting.

On or about March 31, 2025, we began sending the Notice to all stockholders entitled to vote in advance of or during the virtual Annual Meeting. We encourage all of our stockholders to vote on the proposals presented, and we hope the information contained in this document will help you decide how you wish to vote.

In July 2022, the Company completed a business combination pursuant to which ADTRAN, Inc. and Adtran Networks SE, a company organized and existing under the laws of Germany (“Adtran Networks,” formerly ADVA Optical Networking SE), became subsidiaries of the Company (the “Business Combination”). References in this Proxy Statement to “Adtran,” the “Company,” “we,” “our” and “us” refer to ADTRAN, Inc. prior to the Business Combination and to ADTRAN Holdings, Inc. following the Business Combination.

Important Notice Regarding the Availability of Proxy Materials for the

Annual Meeting of Stockholders to be held on May 14, 2025:

This Notice, the Proxy Statement and the 2024 Annual Report to Stockholders of ADTRAN Holdings, Inc. are available free of charge to view, print and download at https://materials.proxyvote.com/00486H.

Additionally, you can find a copy of our Annual Report on Form 10-K for the fiscal year ended December 31, 2024, including financial statements and schedules thereto, on the website of the Securities and Exchange Commission (the “SEC”) at www.sec.gov, or in the “SEC Filings” section of our website athttps://investors.adtran.com. The information on our website is not incorporated by reference into this Proxy Statement or any other report that we file with or furnish to the SEC. You may also obtain a printed copy of our Annual Report on Form 10-K for the fiscal year ended December 31, 2024, including financial statements and schedules thereto, free of charge, from us by sending a written request to: ADTRAN Holdings, Inc., Attn: Corporate Secretary, 901 Explorer Boulevard, Huntsville, Alabama 35806. Exhibits will be provided upon written request.