With the new 4K UHD Blu-ray standard the studios are once again charging you for the upgrade, but many are "faking it" by upscaling 2K films into 4K. While it's true that the 4K UHD standard allows for more beneficial features than purely the upgraded resolution, they are still advertised as 4K which is false advertisement.
Here is an updating list to help you separate the real 4K films from the fake ones. Enjoy the movies!
^ 1. The film was shot mostly in 2.8K mixed with some 5K, with a 4K Digital Intermediate. VFX resolution unknown.
^ 3. VFX was rendered at 2K and upscaled to 4K.
^ 4. VFX done at 2K and upscaled to 4K.
^ 5. 35mm scenes were scanned at 2K, IMAX and final Digital Intermediate were done at 4K.
^ 6. VFX done at 2K and upscaled to 4K.