Yesterday, Apple held the keynote for its WWDC 2017 event, where the company announced iOS 11, macOS 10.13 High Sierra, and watchOS 4. While tvOS was missing, we learned later that Apple will be announcing tvOS 11 tomorrow, although a developer preview is already available.
But if you don't have a paid developer license, you'll no longer have to wait until the fall when it's released to the public. Alongside the usual iOS and macOS public betas, there will now be one for tvOS 11. While the website doesn't say when it will be available, it will presumably be later this month like its iOS and macOS counterparts.
While Apple hasn't formally announced the update yet, we can get a peek at what's coming from the developer preview release notes. tvOS 11 will contain automatic light and dark appearance switching, home screen sync, right-to-left language support, notification support, and a number of under-the-hood improvements.
The final version of tvOS 11 will likely ship this September, around the same time as iOS 11, macOS High Sierra, and watchOS 4. As with the previous version, it will only be available for the fourth-generation Apple TV.