https://www.youtube.com/watch?v=gXqfwX_u7Rs
Quantum Break is not native 4K but could be 1440p or 1080p on XB1X. Its looks better than the original Xbox One version.
Gears of war 4 is native 4K locked 30fps. They said it looks like the PC version running at high settings.
Titanfall 2 has a dynamic resolution that goes above and below 4K. Good improvement over the PS4 Pro version thats capped at 1440p.
Killer Instinct is native 4K 60fps but some video elements does not look good.
F1 2017 is native 4K but the framerate wasn't great.
Path of Exile is 4K 60fps
World of Tanks is native 4K and has stable framerate.
These games were running on the actual Xbox One X.