ADTRAN Holdings, Inc.

Evaluation of Disclosure Controls and Procedures

We maintain disclosure controls and procedures that are designed to ensure that the information required to be disclosed by us in reports that we file or submit under the Securities Exchange Act of 1934, as amended (the "Exchange Act"), is recorded, processed, summarized and reported within the time periods specified in the rules and forms promulgated by the SEC, and that such information is accumulated and communicated to our management, including our Chief Executive Officer and our Chief Financial Officer, as appropriate, to allow timely decisions regarding required disclosure.

As of the end of the period covered by this report, an evaluation was carried out by management, including our Chief Executive Officer and Chief Financial Officer, of the effectiveness of our disclosure controls and procedures (as defined in Rules 13a-15(e) and 15d-15(e)) under the Exchange Act. Based on that evaluation, our Chief Executive Officer and Chief Financial Officer concluded that due to the material weaknesses in our internal control over financial reporting described below, our disclosure controls and procedures were not effective as of September 30, 2026.

Material Weaknesses in Internal Control over Financial Reporting

A material weakness is a deficiency, or a combination of deficiencies, in internal control over financial reporting, such that there is a reasonable possibility that a material misstatement of our annual or interim financial statements will not be prevented or detected on a timely basis. In its assessment of the effectiveness of internal control over financial reporting as of September 30, 2026, management determined that there were deficiencies in Adtran’s internal control over financial reporting that constituted material weaknesses that existed as of September 30, 2026. Such material weaknesses were as follows:

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Adtran did not design and maintain effective controls in response to the risks of material misstatement. Specifically, changes to existing controls or the implementation of new controls have not been sufficient to respond to changes to the risks of material misstatement to financial reporting. This material weakness contributed to the following additional material weakness.

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Adtran did not design and maintain effective controls over financial statement preparation, presentation and disclosure commensurate with its financial reporting requirements. Specifically, Adtran did not design and maintain effective controls over the presentation and disclosure of transactions, including non-controlling interest.

The material weaknesses resulted in the restatements and revision to our consolidated financial statements for the years ended December 31, 2022, 2023 and 2024, as well as the condensed consolidated financial statements for the quarterly and year-to-date periods ended September 30, 2022, March 31, 2023, June 30, 2023, September 30, 2023, March 31, 2024, June 30, 2024 and September 30, 2024. The material weaknesses also resulted in material adjustments that were corrected prior to the issuance of the condensed consolidated financial statements for the quarterly period ended March 31, 2025. Additionally, these material weaknesses could result in misstatements of Adtran’s accounts or disclosures that would result in a material misstatement to the annual or interim consolidated financial statements that would not be prevented or detected.

Management’s Remediation Efforts

To remediate the material weaknesses in Adtran’s internal control over financial reporting related to the risks of material misstatement, and financial statement preparation, presentation and disclosure of transactions including non-controlling interest, Adtran has enhanced existing controls over the review of Adtran’s consolidated financial statements and in the fourth quarter of 2025 completed the implementation of additional financial statement review controls. We believe these enhanced and additional controls operated effectively through the date of this filing. Adtran’s management believes that the continued operation of the activities outlined above in subsequent reporting periods will be effective in remediating such material weaknesses. The material weaknesses cannot be considered remediated until the applicable controls have operated for a sufficient period of time and management has concluded that, through testing, these controls are operating effectively.

Until the remediation steps set forth above, including the implementation of all necessary control activities that we identify, continue to operate effectively for a sufficient amount of time, and there has been time for us to conclude through testing that the control activities have been operating effectively for such time, the material weaknesses described above will not be considered fully remediated.

Changes in Internal Control over Financial Reporting

During the fiscal quarter ended September 30, 2026, Adtran completed the expansion of its SAP enterprise resource planning ("ERP") system, which was previously used by the Adtran Networks SE business, to substantially all of Adtran’s remaining operations. The implementation included the migration of certain financial and operational processes and data from Adtran’s legacy systems to the existing ERP environment.

In connection with the implementation, Adtran modified certain internal controls over financial reporting, including controls and procedures related to transaction processing, financial close and reporting, and the completeness and accuracy of information and reports used in the performance of internal controls. Adtran also updated certain control responsibilities, documentation and procedures to reflect the operation of controls in the expected ERP system.

The implementation and related changes to Adtran's processes and controls are changes in internal control over financial reporting during the most recent fiscal quarter covered by this report that have materially affected, or are reasonably likely to materially affect, Adtran's internal control over financial reporting. Management continues to monitor the operation of the new and modified controls and may make additional changes as Adtran completes post-implementation activities.