Summary of Significant Accounting Policies (Policies)	3 Months Ended
Mar. 31, 2025
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited Condensed Consolidated Financial Statements of ADTRAN Holdings, Inc. and its subsidiaries have been prepared pursuant to the rules and regulations of the SEC applicable to interim financial information presented in Quarterly Reports on Form 10-Q. Accordingly, certain information and notes required by generally accepted accounting principles in the United States of America (“U.S. GAAP”) for complete financial statements are not included herein. The December 31, 2024, Condensed Consolidated Balance Sheet is derived from audited financial statements but does not include all disclosures required by U.S. GAAP for annual financial statements. In the opinion of management, all adjustments necessary to fairly state these interim statements have been recorded and are of a normal and recurring nature. The results of operations for an interim period are not necessarily indicative of the results for the full year. The interim financial statements should be read in conjunction with the consolidated financial statements and notes thereto included in ADTRAN Holdings, Inc. Amendment No. 1 to the Annual Report on Form 10-K for the year ended December 31, 2024, filed with the SEC on May 20, 2025 (the "2024 Form 10-K/A"). Restatement
Restatement of Previously Issued Financial Statements	Restatement of Previously Issued Financial Statements As discussed in the financial statements as of and for the year ended December 31, 2024 included in our amended 2024 Annual Report on Form 10-K/A, we identified errors in our previously issued financial statements. In addition, on May 13, 2025, the Company announced that it needed additional time to complete its quarterly reporting process as a result of the restatements to the annual periods ended December 31, 2023 and 2024 and for the interim periods ended March 31, 2024, June 30, 2024 and September 30, 2024, as well as to complete its evaluation of internal control over financial reporting as of December 31, 2024 as a result of errors related to the historical accounting for certain inventory and cost of goods sold transactions in its Adtran Networks SE subsidiary (the “Adjustment”). As a result, the Company filed a Form 12b-25 with the SEC and delayed the filing of this report. In connection with the identification of the Adjustment, the Audit Committee has overseen an internal investigation into the circumstances surrounding the Adjustment and its impact on the Company’s historical financial statements. Based on the findings of the internal investigation, which is substantially complete, it has been determined that the underlying errors giving rise to the Adjustment were not properly addressed in the Company’s previously filed financial statements as of and for the years ended December 31, 2024 and 2023 and was not communicated to the Audit Committee or the independent auditors prior to the filing of the initial 2024 Annual Report on Form 10-K. As described in Part I, Item 4 of this report, the Company is taking certain remedial actions to address the material weaknesses in its internal controls associated with these findings. The identified errors impacted the Condensed Consolidated Financial Statements as of and for the three months ended March 31, 2024, among other periods as previously disclosed. Below is a summary description of the significant errors in the Company's Condensed Consolidated Financial Statements as of and for the quarter ended March 31, 2024: ADJ 1 - Pursuant to the terms of the DPLTA, each Adtran Networks shareholder (other than the Company) is entitled to receive from us an Annual Recurring Compensation payment of €0.52 per share. The Company erroneously accrued this liability every quarter at €0.59 per share, overstating the associated accrual, the net income attributable to non-controlling interest and the net loss attributable to ADTRAN Holdings, Inc. for fiscal periods beginning with the quarter ended March 31, 2023 through the quarter ended June 30, 2024. ADJ 2 - For the periods beginning with the quarter ended March 31, 2023 through the quarter ended June 30, 2024 the Company remeasured the redeemable non-controlling interest each quarter-end at the current exchange rate of euros to U.S. Dollar. The Company treated the redeemable non-controlling interest as a monetary mezzanine equity instrument but should have treated it as a non-monetary mezzanine equity instrument not subject to remeasurement. ADJ 3 - For the year ended December 31, 2023 through the year ended December 31, 2024, the Company understated cost of revenue and overstated inventory in the Company's Adtran Networks subsidiary due to a system error. In addition, there were adjustments in the Company's U.S and Australian subsidiaries related to inventory reserves that were understated. ADJ 4 - For the year ended December 31, 2023 through the year ended December 31, 2024, the Company understated goodwill and overstated income tax receivable. The understatement was attributable to corrections to goodwill and deferred income tax associated with goodwill for an internal divestiture of a wholly owned subsidiary required by statutory laws in Europe. In addition to the misstatements identified above, the Company has corrected other immaterial errors. These other errors are quantitatively and qualitatively immaterial, individually and in the aggregate. However, the Company has corrected these other errors as part of the correction for the significant errors described above. We assessed the materiality of the errors on prior period consolidated financial statements in accordance with SEC Staff Accounting Bulletin No. 99, “Materiality,” codified in ASC Topic 250, Accounting Changes and Error Corrections. Based on this assessment, we concluded that the errors, in the aggregate, are material to the March 31, 2024 financial statements and therefore, we are restating those financial statements herein. Furthermore, we made adjustments to correct for other previously identified immaterial errors. The Company has also restated impacted amounts within the accompanying footnotes to the Condensed Consolidated Financial Statements. See Note 18 for further information about the restatement
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expense during the reporting period. Significant estimates include allowance for credit losses on accounts receivable and contract assets, excess and obsolete inventory reserves, warranty reserves, customer rebates, determination and accrual of the deferred revenue related to performance obligations under contracts with customers, estimated costs to complete obligations associated with deferred and accrued revenue and network installations, estimated income tax provision and income tax contingencies, fair value of stock-based compensation, assessment of goodwill and other intangibles for impairment, estimated lives of intangible assets, estimates of intangible assets upon measurement, estimated pension liability and fair value of investments and estimated contingent liabilities. Actual amounts could differ significantly from these estimates. We assessed certain accounting matters that generally require consideration of forecasted financial information in context with the information reasonably available to us and the unknown future impacts of ongoing inflationary pressures, continued elevated interest rates, currency fluctuations and political tensions as of March 31, 2025, and through the date of this report. These conditions could result in further impacts to the Company's consolidated financial statements in future reporting periods. The accounting matters assessed included, but were not limited to, the allowance for credit losses, stock-based compensation, carrying value of goodwill, intangibles and other long-lived assets, financial assets, valuation allowances for tax assets, revenue recognition and costs of revenue.
Recent Accounting Pronouncements Not Yet Adopted	Recent Accounting Pronouncements Not Yet Adopted In November 2024, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update ("ASU") 2024-03, "Disaggregation of Income Statement Expenses (DISE) (Topic 220): Improvements to Income Statement Disclosures", which applies to all public business entities (PBEs) and is intended to enhance disclosures about specific types of expenses included in the expense captions presented on the face of the income statement as well as disclosures about selling expenses. The amendments are effective prospectively for annual periods beginning after December 15, 2026, and early adoption and retrospective application are permitted. The Company is currently evaluating the effect that adoption of ASU 2024-03 will have on our disclosures. In December 2023, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update ("ASU") 2023-09, "Income Taxes (Topic 740): Improvements to Income Tax Disclosures", which is intended to enhance the transparency, decision usefulness and effectiveness of income tax disclosures. The amendments in this ASU require a public entity to disclose a tabular tax rate reconciliation, using both percentages and currency, with specific categories. A public entity is also required to provide a qualitative description of the states and local jurisdictions that make up the majority of the effect of the state and local income tax category and the net amount of income taxes paid, disaggregated by federal, state and foreign taxes and also disaggregated by individual jurisdictions. The amendments also remove certain disclosures that are no longer considered cost beneficial. The amendments are effective prospectively for annual periods beginning after December 15, 2024, and early adoption and retrospective application are permitted. The Company is currently evaluating the effect that adoption of ASU 2023-09 will have on our disclosures.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements There are currently no recently adopted accounting pronouncements that are expected to have a material effect on the Condensed Consolidated Financial Statements.
Reclassification of Prior Year Presentation	Reclassification of Prior Year Presentation Certain prior year amounts have been reclassified for consistency with current year presentation. These reclassifications had no effect on reported results of operations. An adjustment has been made to the Consolidated Statement of Cash Flows for the quarter ended March 31, 2024, to reclassify between Property, Plant and Equipment and Intangible Assets.

Summary of Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2025

The accompanying unaudited Condensed Consolidated Financial Statements of ADTRAN Holdings, Inc. and its subsidiaries have been prepared pursuant to the rules and regulations of the SEC applicable to interim financial information presented in Quarterly Reports on Form 10-Q. Accordingly, certain information and notes required by generally accepted accounting principles in the United States of America (“U.S. GAAP”) for complete financial statements are not included herein. The December 31, 2024, Condensed Consolidated Balance Sheet is derived from audited financial statements but does not include all disclosures required by U.S. GAAP for annual financial statements.

In the opinion of management, all adjustments necessary to fairly state these interim statements have been recorded and are of a normal and recurring nature. The results of operations for an interim period are not necessarily indicative of the results for the full year. The interim financial statements should be read in conjunction with the consolidated financial statements and notes thereto included in ADTRAN Holdings, Inc. Amendment No. 1 to the Annual Report on Form 10-K for the year ended December 31, 2024, filed with the SEC on May 20, 2025 (the "2024 Form 10-K/A").

Restatement

Restatement of Previously Issued Financial Statements

As discussed in the financial statements as of and for the year ended December 31, 2024 included in our amended 2024 Annual Report on Form 10-K/A, we identified errors in our previously issued financial statements. In addition, on May 13, 2025, the Company announced that it needed additional time to complete its quarterly reporting process as a result of the restatements to the annual periods ended December 31, 2023 and 2024 and for the interim periods ended March 31, 2024, June 30, 2024 and September 30, 2024, as well as to complete its evaluation of internal control over financial reporting as of December 31, 2024 as a result of errors related to the historical accounting for certain inventory and cost of goods sold transactions in its Adtran Networks SE subsidiary (the “Adjustment”). As a result, the Company filed a Form 12b-25 with the SEC and delayed the filing of this report.

In connection with the identification of the Adjustment, the Audit Committee has overseen an internal investigation into the circumstances surrounding the Adjustment and its impact on the Company’s historical financial statements. Based on the findings of the internal investigation, which is substantially complete, it has been determined that the underlying errors giving rise to the Adjustment were not properly addressed in the Company’s previously filed financial statements as of and for the years ended December 31, 2024 and 2023 and was not communicated to the Audit Committee or the independent auditors prior to the filing of the initial 2024 Annual Report on Form 10-K. As described in Part I, Item 4 of this report, the Company is taking certain remedial actions to address the material weaknesses in its internal controls associated with these findings.

The identified errors impacted the Condensed Consolidated Financial Statements as of and for the three months ended March 31, 2024, among other periods as previously disclosed. Below is a summary description of the significant errors in the Company's Condensed Consolidated Financial Statements as of and for the quarter ended March 31, 2024:

ADJ 1 - Pursuant to the terms of the DPLTA, each Adtran Networks shareholder (other than the Company) is entitled to receive from us an Annual Recurring Compensation payment of €0.52 per share. The Company erroneously accrued this liability every quarter at €0.59 per share, overstating the associated accrual, the net income attributable to non-controlling interest and the net loss attributable to ADTRAN Holdings, Inc. for fiscal periods beginning with the quarter ended March 31, 2023 through the quarter ended June 30, 2024.

ADJ 2 - For the periods beginning with the quarter ended March 31, 2023 through the quarter ended June 30, 2024 the Company remeasured the redeemable non-controlling interest each quarter-end at the current exchange rate of euros to U.S. Dollar. The Company treated the redeemable non-controlling interest as a monetary mezzanine equity instrument but should have treated it as a non-monetary mezzanine equity instrument not subject to remeasurement.

ADJ 3 - For the year ended December 31, 2023 through the year ended December 31, 2024, the Company understated cost of revenue and overstated inventory in the Company's Adtran Networks subsidiary due to a system error. In addition, there were adjustments in the Company's U.S and Australian subsidiaries related to inventory reserves that were understated.

ADJ 4 - For the year ended December 31, 2023 through the year ended December 31, 2024, the Company understated goodwill and overstated income tax receivable. The understatement was attributable to corrections to goodwill and deferred income tax associated with goodwill for an internal divestiture of a wholly owned subsidiary required by statutory laws in Europe.

In addition to the misstatements identified above, the Company has corrected other immaterial errors. These other errors are quantitatively and qualitatively immaterial, individually and in the aggregate. However, the Company has corrected these other errors as part of the correction for the significant errors described above.

We assessed the materiality of the errors on prior period consolidated financial statements in accordance with SEC Staff Accounting Bulletin No. 99, “Materiality,” codified in ASC Topic 250, Accounting Changes and Error Corrections. Based on this assessment, we concluded that the errors, in the aggregate, are material to the March 31, 2024 financial statements and therefore, we are restating those financial statements herein. Furthermore, we made adjustments to correct for other previously identified immaterial errors. The

Company has also restated impacted amounts within the accompanying footnotes to the Condensed Consolidated Financial Statements. See Note 18 for further information about the restatement

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expense during the reporting period. Significant estimates include allowance for credit losses on accounts receivable and contract assets, excess and obsolete inventory reserves, warranty reserves, customer rebates, determination and accrual of the deferred revenue related to performance obligations under contracts with customers, estimated costs to complete obligations associated with deferred and accrued revenue and network installations, estimated income tax provision and income tax contingencies, fair value of stock-based compensation, assessment of goodwill and other intangibles for impairment, estimated lives of intangible assets, estimates of intangible assets upon measurement, estimated pension liability and fair value of investments and estimated contingent liabilities. Actual amounts could differ significantly from these estimates.

We assessed certain accounting matters that generally require consideration of forecasted financial information in context with the information reasonably available to us and the unknown future impacts of ongoing inflationary pressures, continued elevated interest rates, currency fluctuations and political tensions as of March 31, 2025, and through the date of this report. These conditions could result in further impacts to the Company's consolidated financial statements in future reporting periods. The accounting matters assessed included, but were not limited to, the allowance for credit losses, stock-based compensation, carrying value of goodwill, intangibles and other long-lived assets, financial assets, valuation allowances for tax assets, revenue recognition and costs of revenue.

Recent Accounting Pronouncements Not Yet Adopted

In November 2024, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update ("ASU") 2024-03, "Disaggregation of Income Statement Expenses (DISE) (Topic 220): Improvements to Income Statement Disclosures", which applies to all public business entities (PBEs) and is intended to enhance disclosures about specific types of expenses included in the expense captions presented on the face of the income statement as well as disclosures about selling expenses. The amendments are effective prospectively for annual periods beginning after December 15, 2026, and early adoption and retrospective application are permitted. The Company is currently evaluating the effect that adoption of ASU 2024-03 will have on our disclosures.

In December 2023, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update ("ASU") 2023-09, "Income Taxes (Topic 740): Improvements to Income Tax Disclosures", which is intended to enhance the transparency, decision usefulness and effectiveness of income tax disclosures. The amendments in this ASU require a public entity to disclose a tabular tax rate reconciliation, using both percentages and currency, with specific categories. A public entity is also required to provide a qualitative description of the states and local jurisdictions that make up the majority of the effect of the state and local income tax category and the net amount of income taxes paid, disaggregated by federal, state and foreign taxes and also disaggregated by individual jurisdictions. The amendments also remove certain disclosures that are no longer considered cost beneficial. The amendments are effective prospectively for annual periods beginning after December 15, 2024, and early adoption and retrospective application are permitted. The Company is currently evaluating the effect that adoption of ASU 2023-09 will have on our disclosures.

Recently Adopted Accounting Pronouncements

There are currently no recently adopted accounting pronouncements that are expected to have a material effect on the Condensed Consolidated Financial Statements.

Reclassification of Prior Year Presentation

Certain prior year amounts have been reclassified for consistency with current year presentation. These reclassifications had no effect on reported results of operations. An adjustment has been made to the Consolidated Statement of Cash Flows for the quarter ended March 31, 2024, to reclassify between Property, Plant and Equipment and Intangible Assets.