The update will start rolling out at 12:01 AM PDT, but backwards compatibility support won't come for another 12 hours.
The New Xbox One Experience dashboard update will start rolling out worldwide at 12:01 AM PDT / 3:01 AM EDT on Thursday, November 12, Microsoft has announced. In a blog post, Microsoft's Larry "Major Nelson" Hryb explained that it will be a phased deployment, meaning not everyone will get it at the same time.
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Xbox One owners who have the Instant-on power mode enabled won't have to do anything, as the console will automatically download the update when it becomes available. People using the Energy-saving mode, however, will need to go to Settings -- System to check if the update is available. If it is, you can then select "Update Now" to initiate it.

Hyrb also points out that the New Xbox One Experience's backwards compatibility support for Xbox 360 titles won't start right away. It won't become available until sometime after 12:01 PM PDT / 3:01 PM EDT on November 12, Hryb said.
f you don't want to download the New Xbox One Experience, you don't have to right away. But come November 23, all Xbox One consoles will receive a prompt for a mandatory update if they have not updated to the New Xbox One Experience.

Check back on November 12 for lots more on the New Xbox One Experience.

Further reading: All 104 Xbox 360 Games Playable on Xbox One Via Backwards Compatibility
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