Avengers: Endgame was shot digitally primarily on the ARRI ALEXA 65, a camera capable of native 6.5K resolution. However, like almost all major Hollywood releases, the film underwent a 4K Digital Intermediate (DI) process. This means the 4K UHD disc isn't a pure 6K downscale, but rather the studio-approved master.
The standout feature of the 4K release is the exclusive track. avengers endgame 4k blu-ray