HOW TO GET IT:
• If your console is in Instant-On mode and you have been selected to receive the update, it will download and install the update and reboot to standby.
• NOTE: Once the update is available to you, you can manually begin the update by launching the Guide and navigating to All Settings > System > Updates.
• If your console hasn’t downloaded and installed the update by 1:00 AM PST 11/29/2017 (9:00AM GMT 29/11), you will be prompted to do so at that time.
• NOTE: This update has a shorter than usual amount of time before it becomes mandatory.
OS version released: rs3_release_xbox_dev_1711.171121-1645
Available: 2:00PM PST 11/28 (10:00PM GMT 28/11)
Fixed issues which sometimes caused the Guide to unexpectedly crash.
Fixed issues which could cause games to fail to install.
•Streaming Video Fixes
Fixed issues which some streaming video aps would fail to show video and ads.
• The left and right navigation for selecting date and time during Tournament creation is currently reversed when the console language is set to Arabic or Hebrew.
• Left and right navigation in Tournament twists is reversed when the console language is set to Arabic or Hebrew.
• Left and right navigation in the bracket view of Tournaments is reversed when the console language is set to Arabic or Hebrew.
• Avatars on Home
Users wishing to represent themselves as an avatar can do so by changing their settings under My profile > Customize profile > Show my avatar.
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Quelle: Xbox Insider Forum