Shares of Amentum Holdings, Inc. (AMTM) plunged 5.89% in after-hours trading on Monday, as investors reacted to the company's fiscal third-quarter 2026 results that fell short of revenue expectations and included a cut to its full-year revenue outlook.

The company reported quarterly revenue of $3.49 billion, missing the consensus estimate of $3.57 billion. While adjusted earnings per share of $0.67 beat analyst forecasts, and adjusted EBITDA rose 6% to $290 million, the topline miss overshadowed the positive metrics. Amentum also revised its fiscal 2026 revenue guidance downward to $13.8 billion-$13.95 billion, from the prior range of $13.95 billion-$14.3 billion, citing contract transitions and prior-year divestitures as headwinds. The company raised its adjusted EBITDA and adjusted EPS outlook, but the weaker revenue trajectory weighed on sentiment.

The stock's decline reflected market disappointment with the revenue shortfall, as growth in critical digital infrastructure and space systems was not enough to offset the impact of contract transitions to unconsolidated joint ventures.