UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

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Your Vote Counts ADTRAN HOLDINGS, INC. 2024 Annual Meeting Vote by May 7, 2024 11:59 PM ET. For shares held in a Plan, vote by May 6, 2024 11:59 PM ET. ADTRAN HOLDINGS, INC. 901 EXPLORER BOULEVARD HUNTSVILLE, AL 35806 V29921-P04942 You invested in ADTRAN HOLDINGS, INC. and it’s time to vote! You have the right to vote on proposals being presented at the Annual Meeting. This is an important notice regarding the availability of proxy material for the stockholder meeting to be held on May 8, 2024. Get informed before you vote View the Notice and Proxy Statement for the 2024 Annual Meeting and the 2023 Annual Report online OR you can receive a free paper or email copy of the material(s) by requesting prior to April 24, 2024. If you would like to request a copy of the material(s) for this and/or future stockholder meetings, you may (1) visit www.ProxyVote.com, (2) call 1-800-579-1639 or (3) send an email to sendmaterial@proxyvote.com. If sending an email, please include your control number (indicated below) in the subject line. Unless requested, you will not otherwise receive a paper or email copy. For complete information and to vote, visit www.ProxyVote.com Control # Smartphone users Vote Virtually at the Meeting* Point your camera here and May 8, 2024 10:30 a.m., Central Time vote without entering a control number Virtually at: www.virtualshareholdermeeting.com/ADTN2024 *Please check the meeting materials for any special requirements for meeting attendance.

Vote at www.ProxyVote.com THIS IS NOT A VOTABLE BALLOT This is an overview of the proposals being presented at the upcoming stockholder meeting. Please follow the instructions on the reverse side to vote these important matters. Board Voting Items Recommends 1. Election of Directors Nominees: 1a. Thomas R. Stanton For 1b. H. Fenwick Huss For 1c. Gregory J. McCray For 1d. Balan Nair For 1e. Brian Protiva For 1f. Jacqueline H. Rice For 1g. Nikos Theodosopoulos For 1h. Kathryn A. Walker For 2. Approval of the ADTRAN Holdings, Inc. 2024 Employee Stock Incentive Plan. For 3. Approval of the ADTRAN Holdings, Inc. 2024 Directors Stock Plan. For 4. Non-binding advisory vote to approve the compensation of the Company’s named executive officers. For 5. Ratification of the appointment of PricewaterhouseCoopers LLP as the independent registered public accounting firm For of the Company for the fiscal year ending December 31, 2024. NOTE: Such other business as may properly come before the meeting or any adjournment thereof. Prefer to receive an email instead While voting on www.ProxyVote.com, be sure to click Delivery Settings. V29922-P04942