EXHIBIT 99.1 ADTRAN Holdings, Inc. reports preliminary fourth quarter 2023 financial results • Preliminary Q4 revenue at $225.5 million and at mid-point of guidance • Sequential improvement in preliminary GAAP and non-GAAP operating expenses in Q4, with a 7.6% reduction in GAAP operating expenses and a 15.1% reduction in non-GAAP operating expenses respectively Huntsville, Alabama, USA. — February 26, 2024 — ADTRAN Holdings, Inc. (NASDAQ: ADTN and FSE: QH9) (“ADTRAN Holdings” or the “Company”) today announc ...