tvOS 9.1 launches for new Apple TV with Siri search for Apple Music
The new fourth-generation Apple TV received a software update on Tuesday, with the tvOS 9.1 update giving users the ability to search for music with their voice and the Siri Remote.

tvOS 9.1 can be downloaded by opening the Apple TV Settings app, choosing System, and then Software Updates under the Maintenance subheading.
tvOS 9.1 adds support for Siri searches in the Apple Music service. Release notes for tvOS updates are not provided by Apple, making the extensive list of improvements and changes unknown.
Digging around in the tvOS code, developers have also found evidence of support for app folders. As of yet, folders are not available in tvOS 9.1.
A total of three betas for tvOS 9.1 were issued before Tuesday's public release. It also launches alongside iOS 9.2 and OS X 10.11.2.
tvOS 9.1 is the second update for the fourth-generation Apple TV, which launched in late October. The previous update, tvOS 9.0.1, debuted in November with minor bug fixes.

tvOS 9.1 can be downloaded by opening the Apple TV Settings app, choosing System, and then Software Updates under the Maintenance subheading.
tvOS 9.1 adds support for Siri searches in the Apple Music service. Release notes for tvOS updates are not provided by Apple, making the extensive list of improvements and changes unknown.
Digging around in the tvOS code, developers have also found evidence of support for app folders. As of yet, folders are not available in tvOS 9.1.
A total of three betas for tvOS 9.1 were issued before Tuesday's public release. It also launches alongside iOS 9.2 and OS X 10.11.2.
tvOS 9.1 is the second update for the fourth-generation Apple TV, which launched in late October. The previous update, tvOS 9.0.1, debuted in November with minor bug fixes.
Comments
Out of the box, my ATV4 controlled my receiver's volume over HDMI perfectly. Since updating to 9.1 this evening, the ATV4 now controls the volume of the TV via IR. I can force it to control the receiver over IR, but I can no longer control either device's volume over HDMI. I've tried all combinations of settings under Settings > Remotes and Devices > Home Theater Control.
UPDATE: After power-cycling all components, control of my receiver's volume over HDMI is now working again.
Other commands like adding a song to up next and shuffling a playlist work great though.