The New Xbox One Experience should now be available to all preview members who opted in as of today.
Previously only available to a select few members, the updated interface will be available to all preview members who opted in back in September when it was first released, with the final version being released publicly sometime in November.
The new interface features a slew of changes, including the incredibly exciting Xbox 360 backwards compatibility. Other changes include an allegedly faster and more intuitive interface, and various community features to promote a more social environment on the console, including a recently released community calendar that schedules game releases, live streams, and events to meet other players.