ADTRAN Holdings, Inc.

2026 Annual Meeting of Stockholders

As previously disclosed in the Company’s Current Report on Form 8-K filed with the SEC on July 30, 2025, on July 29, 2025, the Board set the date for the Company’s 2026 Annual Meeting as May 13, 2026. The meeting will be a virtual meeting conducted by live webcast on the internet. Additional details regarding the 2026 Annual Meeting, including the time and matters to be voted upon, will be set forth in the Company’s definitive proxy statement for the 2026 Annual Meeting to be filed with the SEC.

As the date of the 2026 Annual Meeting has changed by more than 30 days from the one-year anniversary of the 2025 Annual Meeting, the Company is informing stockholders of this change in accordance with Rule 14a-5(f) under the Exchange Act, and it is also informing stockholders of the new dates described below for submitting stockholder proposals and other matters.

Pursuant to Rule 14a-8 of the Exchange Act, any stockholder intending to present a proposal for inclusion in the proxy statement for the 2026 Annual Meeting must provide timely written notice of the proposal to us at ADTRAN Holdings, Inc., Attn: Corporate Secretary, 901 Explorer Boulevard, Huntsville, Alabama 35806, along with proof of ownership of our stock in accordance with Rule 14a‑8(b)(2). The Company must receive the proposal by December 1, 2025 for possible inclusion in the proxy statement, which the Board has determined to be a reasonable time before the Company expects to begin to print and send its proxy materials in accordance with Rule 14a-8(e). The December 1, 2025 deadline also applies in determining whether notice of a shareholder proposal is timely for purposes of exercising discretionary voting authority with respect to proxies under Rule 14a-4(c)(1) of the Exchange Act.

Additionally, under the Company’s bylaws, any stockholder of record intending to nominate a candidate for election to the Board or to propose any business at the 2026 Annual Meeting must give timely written notice to us at ADTRAN Holdings, Inc., Attn: Corporate Secretary, 901 Explorer Boulevard, Huntsville, Alabama 35806. A nomination or proposal for the 2026 Annual Meeting will be considered timely if it is received no earlier than January 13, 2026 (the 120th day prior to the 2026 Annual Meeting) and no later than the close of business on February 12, 2026 (the later of the 90th day prior to the 2026 Annual Meeting and the 10th day following the day on which public announcement of the date of the 2026 Annual Meeting is first made). In no event shall the adjournment or postponement of the 2026 Annual Meeting commence a new time period (or extend any time period) for the giving of a stockholder’s notice with respect to a nomination or proposal for the 2026 Annual Meeting. The notice of nomination or proposal, including any notice of a proposal for inclusion in the proxy statement described in the paragraph above, must detail the information specified in the Company’s bylaws and comply with Delaware law and the applicable rules of the SEC. The Company will not entertain any proposals or nominations at the 2026 Annual Meeting that do not meet the requirements set forth in its bylaws. In addition to satisfying the requirements under our bylaws, to comply with the SEC’s universal proxy rules, stockholders who intend to solicit proxies in support of director nominees other than the Company’s nominees at the 2026 Annual Meeting must provide notice to the Company that complies with the informational requirements of Rule 14a-19 under the Exchange Act.

(a) Not applicable

(b) Not applicable

(c) Insider Trading Arrangements

During the fiscal quarter ended June 30, 2025, none of the Company’s directors or executive officers adopted or terminated any contract, instruction or written plan for the purchase or sale of Company securities that was intended to satisfy the affirmative defense conditions of Rule 10b5-1(c) or any “non-Rule 10b5-1 trading arrangement.”