Amentum Holdings, Inc. (AMTM) experienced a significant 24-hour plunge of 11.15%, with the sharp decline occurring in post-market trading on Monday following the release of its first-quarter fiscal 2026 earnings report.

The company reported adjusted earnings per share of $0.54, which exceeded analyst estimates of $0.52. However, quarterly revenue of $3.237 billion fell short of the $3.340 billion consensus estimate and represented a 5.24% decline compared to the same period last year.

While Amentum reaffirmed its full-year guidance, the revenue miss and year-over-year sales decrease appear to have driven investor concern, leading to substantial selling pressure in extended trading hours.