From their own site:
https://news.xbox.com/2017/06/11/new-packaging-icons-xbox/
Despite their claims about "true 4K" and thus not competing with the pro, they're using the same techniques.
The Assassin's Creed Origins director confirms here that the game will be dynamic 4k on XB1X:
https://www.youtube.com/watch?v=FtllzLCt1WY
Edit: there seems to be some confusion. Yes, this is old news for some but clearly new to others going by posts in this thread. Also, this thread is a reaction to Spencer's comments from recent interviews, as explained here:
For the record, I don't think there's anything wrong with checkerboarding or even dynamic 4K. I think they're fine techniques. I also think a "native 4k mandate for all games" would be a bad idea anyway.