A new Xbox OS update has gone live and appears to be available to the entire Xbox One family of consoles. It should improve 4K performance as well as improvements to Cortana, the Dashboard and My Games & Apps.
Here's the release notes from Xbox:
AudioThe update is available now. On a standard Xbox One at least, it clocks in at around 440MB.
Added reliability fixes to Cortana.
Unplugging a headset during video playback no longer results in audio loss before video playback freezes.
Made audio system upgrades when switching from Home to a game or app.
Improved Cortana responsiveness to commands.
Fixed an issue that caused some consoles to crash unexpectedly.
Improved performance on the Home Dashboard.
Improved mouse responsiveness to reduce lag.
My games and apps
Improved the installation experience for various FastStart titles.
Fixed a problem in some games (e.g. Resident Evil 0) in which cutscenes would fail and the game would lock.
Fixes an issue to ensure certain apps like the Avatar Editor and Microsoft Rewards work on first launch.
Fixed an issue in which some people received the E203 error when taking a system update.
Improved performance on the network port.
Improved performance and reliability on the save game feature when games are suspended.
Improved speed and performance of My games & apps.
Improved idle screen performance.
Improved 4K visual performance in games.
Improved the performance of the guide on Home.
Made improvements to the 4K video pipeline so that apps like Netflix display 4K content correctly.