If you haven't noticed yet, the New Xbox One Experience, complete with backwards compatibility functionality, officially rolled out today.
As of 3:01am ET / 12:01am PT, the console's biggest update yet began rolling out to all Xbox One owners, but it's important to note that not everyone will get the update at once. Because it's deploying globally, it might take a while for you to receive it.
If you use Instant-on power mode, your Xbox One should download the update in the background when you put your console into Connected Standby mode when its ready. If your console is in Energy-saving mode, you'll need to initiate the download and update process through the Settings menu.
The update is pretty massive, checking in just shy of 1.2GB, but that's to be expected considering all the improvements and features it brings. While backwards compatibility is the main attraction, the New Xbox One Experience also brings an improved store, revamped OneGuide, the return of Avatars, and much more.