Forza 7 was the only firstparty game running in native 4K on Xbox One X, during the E3 conference

[jason1637]

http://gearnuke.com/crackdown-3-will-run-true-4k-60-fps-xbox-one-x-30-fps-xbox-one/
Crackdown 3 was running Native 4K and Microsoft confirmed that all of their games will run native 4K on the Xbox One X.