Overview

• Block 4 is being reorganized into a smaller major subprogram expected to include fewer capabilities, with acquisition planning due this fall and completion not likely before 2031.
• GAO reports total Block 4 costs have risen by more than $6 billion, with an updated official estimate expected later in 2025.
• In 2024, Lockheed Martin delivered 110 jets an average of 238 days late and Pratt & Whitney delivered 123 engines late, reflecting persistent schedule problems.
• TR‑3, a $1.9 billion hardware and software package, was the primary cause of late aircraft deliveries, while the F135 core upgrade is not expected in production until at least 2031, pushing some follow‑on capabilities to 2033.
• GAO issued six recommendations to evaluate delivery capacity, tighten on‑time incentive fees that allowed payment despite lateness, and expand iterative, digital development practices, and DOD concurred with four and partially concurred with two.