Future Block 4 capabilities are intended to bring the F-35 better sensors, improved sensor integration, and the ability to carry more and deadlier weapons.
The U.S. is in a race to field the capability and develop systems to defend against hypersonic missiles, which China and Russia are developing and testing.
Experts say it's unlikely the Air Force could save $15 billion only targeting the kind of diversity and climate change programs Sec. Hegseth has derided.
The Space Force is evaluating what systems it already has in development to support President Trump's order and what capabilities it would need to build.
Work continues on the engines that might one day power the Next Generation Air Dominance fighter, though the fate of NGAD itself is still undetermined.