CTO — Christoph Glingener: The filing describes an amendment to an existing employment agreement regarding compensation terms, not a change in personnel or management structure.

Results of Operations and Financial Condition. On August 3, 2026, ADTRAN Holdings, Inc. (“ADTRAN”) announced its financial results for the second quarter ended June 30, 2026. A copy of ADTRAN’s press release announcing its financial results is attached as Exhibit 99.1 hereto and incorporated by reference herein.

Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant The information in

Entry into a Material Definitive Agreement. On July 21, 2026, ADTRAN Holdings, Inc. (the “Company”) as guarantor, ADTRAN, Inc., a Delaware corporation (the “US Borrower”), and Adtran Networks SE, a European stock corporation (the “German Borrower” and together with the US Borrower, collectively, the “Borrowers”), entered into a credit agreement (the “Credit Agreement”) with JPMorgan Chase Bank, N.A., as administrative agent for the US Borrower and J.P. Morgan SE, as administrative agent for t…

Termination of a Material Definitive Agreement. The information in

Results of Operations and Financial Condition. On July 21, 2026, ADTRAN Holdings, Inc. (“ADTRAN”) announced certain preliminary financial results for the fiscal quarter ended June 30, 2026. A copy of ADTRAN’s press release announcing certain preliminary financial results is attached as Exhibit 99.1 hereto and incorporated by reference in this

Director — Anne DelSanto: The Board increased its size and elected Anne DelSanto as a new director.

Results of Operations and Financial Condition. On May 4, 2026, ADTRAN Holdings, Inc. (“ADTRAN”) announced its financial results for the first quarter ended March 31, 2026. A copy of ADTRAN’s press release announcing its financial results is attached as Exhibit 99.1 hereto and incorporated by reference herein.

Amendments to employment agreements and grants of long-term financial plan PSU awards.

Results of Operations and Financial Condition. On February 25, 2026, ADTRAN Holdings, Inc. (“ADTRAN”) announced its financial results for the quarter and fiscal year ended December 31, 2025. A copy of ADTRAN’s press release announcing its financial results is attached as Exhibit 99.1 hereto and incorporated by reference herein.

Results of Operations and Financial Condition. On January 21, 2026, ADTRAN Holdings, Inc. (“ADTRAN”) announced certain preliminary financial results for the fiscal quarter and year ended December 31, 2025. A copy of ADTRAN’s press release announcing certain preliminary financial results is attached as Exhibit 99.1 hereto and incorporated by reference in this

Chief Technology Officer (CTO) — Christoph Glingener: The employment agreement was amended to extend the term, increase salary, and provide details on incentive bonuses and equity grants.

Results of Operations and Financial Condition. On November 3, 2025, ADTRAN Holdings, Inc. (“ADTRAN”) announced its financial results for the third quarter ended September 30, 2025. A copy of ADTRAN’s press release announcing its financial results is attached as Exhibit 99.1 hereto and incorporated by reference herein.

The Notes were issued to the Initial Purchasers in reliance upon Section 4(a)(2) of the Securities Act of 1933, as amended (the “Securities Act”) in transactions not involving any public offering. The Notes were resold by the Initial Purchasers to persons whom the Initial Purchasers reasonably believe are “qualified institutional buyers,” as defined in, and in accordance with, Rule 144A under the Securities Act. Any shares of the Company’s common stock that may be issued upon conversion of th…

Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant. The disclosure set forth in

Entry into a Material Definitive Agreement. Indenture and Notes On September 19, 2025, ADTRAN Holdings, Inc. (the “Company”) issued $201,250,000 aggregate principal amount of its 3.75% convertible senior notes due 2030 (the “Notes”). The Notes were issued pursuant to, and are governed by, an indenture (the “Indenture”), dated as of September 19, 2025, between the Company and U.S. Bank Trust Company, National Association, as trustee (the “Trustee”). Pursuant to the purchase agreement between t…

Other Events. Convertible Senior Notes Offering On September 17, 2025, ADTRAN Holdings, Inc. (the “Company”) issued a press release announcing the pricing of its upsized offering (the “Offering”) of $175.0 million aggregate principal amount of convertible senior notes due 2030 (the “Notes”), and the related grant to the initial purchasers of the Notes of an option to purchase up to an additional $26.25 million aggregate principal amount of the Notes in the Offering. The Notes will be sold to…

Entry into a Material Definitive Agreement Sixth Amendment to the Wells Fargo Credit Agreement On September 16, 2025, ADTRAN Holdings, Inc. (the “Company”), the Company’s wholly-owned direct subsidiary, Adtran, Inc. (the “U.S. Borrower”), the Company’s non-wholly-owned direct subsidiary, Adtran Networks SE (the “German Borrower”), the lenders party thereto and Wells Fargo Bank, National Association, as administrative agent (the “Administrative Agent”), entered into the Sixth Amendment and Con…

Results of Operations and Financial Condition. On August 4, 2025, ADTRAN Holdings, Inc. (“ADTRAN”) announced its financial results for the second quarter ended June 30, 2025. A copy of ADTRAN’s press release announcing its financial results is attached as Exhibit 99.1 hereto and incorporated by reference herein.

Results of Operations and Financial Condition. On July 16, 2025, ADTRAN Holdings, Inc. (“ADTRAN”) announced its preliminary revenue for the fiscal quarter ended June 30, 2025. A copy of ADTRAN’s press release announcing ADTRAN's preliminary revenue is attached as Exhibit 99.1 hereto and incorporated by reference herein.

Results of Operations and Financial Condition. On July 16, 2025, ADTRAN Holdings, Inc. (“ADTRAN”) announced its preliminary revenue for the fiscal quarter ended June 30, 2025. A copy of ADTRAN’s press release announcing ADTRAN's preliminary revenue is attached as Exhibit 99.1 hereto and incorporated by reference herein.

Results of Operations and Financial Condition. Updated Non-GAAP Financial Measures and Updated Investor Presentation On May 20, 2025, ADTRAN Holdings, Inc. (the “Company”) filed with the Securities and Exchange Commission (the “SEC”) an Amendment No. 1 to its Annual Report on Form 10-K for the fiscal year ended December 31, 2024 (the “Amended Form 10-K”), in which the Company restated its consolidated financial statements as of and for the fiscal years ended December 31, 2024 and 2023 and cer…

Non-Reliance on Previously Issued Financial Statements or a Related Audit Report or Completed Interim Review. As previously disclosed by ADTRAN Holdings, Inc. (the “Company”) in its Current Report on Form 8-K furnished to the Securities and Exchange Commission (“SEC”) on April 16, 2025 (the “Form 8-K”), the Company’s majority-owned subsidiary, Adtran Networks SE (“Networks”), published an ad hoc notification in Germany on April 15, 2025 (the “Ad Hoc Notification”). The Ad Hoc Notification dis…

Entry into a Material Definitive Agreement. On May 6, 2025, ADTRAN Holdings, Inc. (the “Company”), the Company’s wholly-owned direct subsidiary, ADTRAN, Inc. (the “US Borrower”), the Company’s non-wholly-owned direct subsidiary, Adtran Networks SE (the “German Borrower”), the lenders party thereto and Wells Fargo Bank, National Association, as administrative agent (the “Administrative Agent”), entered into a Fifth Amendment to Credit Agreement (“Amendment No. 5”), which amends that certain Cr…

Results of Operations and Financial Condition. On May 7, 2025, ADTRAN Holdings, Inc. (“ADTRAN”) announced its preliminary financial results for the first quarter ended March 31, 2025. A copy of ADTRAN’s press release announcing its preliminary financial results is attached as Exhibit 99.1 hereto and incorporated by reference herein.