Today, Apple released its latest update for the fourth- and fifth-generation Apple TV, bringing the OS to tvOS 11.2. It's been in beta for just over a month, along with iOS 11.2, macOS 10.13.2 High Sierra, and watchOS 4.2. iOS 11.2 ended up being released over the weekend, which is particularly odd since Apple usually releases all four at the same time.
tvOS 11.2 contains new options for dynamically changing HDR and frame rate based on the content that you're watching. To turn this on or off, go to your Video and Audio settings and go to 'Match Content', and you can choose between matching dynamic range and matching frame rate.
There's also a new Sports section included in the TV app. It integrates with the ESPN app to allow users to watch live sports.
That's about all that's new. Security details of the update are coming "soon", as are details for iOS 11.2. watchOS 4.2 and macOS 10.13.2 are still listed as being in beta, but we should see those within the next couple of days.