Registered developers can download the tvOS 11 update by connecting the Apple TV to a computer with a USB-C cable and installing the beta software using iTunes.
tvOS 11 didn't receive a lot of attention at the Worldwide Developers Conference because it's a modest update, but according to Apple's release notes, it does introduce a few new features to the operating system.
tvOS 11 brings automatic switching between light/dark mode based on local time, Home screen syncing options that keep multiple Apple TVs in a household in sync, new background modes and notification support, Focus API improvements, custom sound support, network-based pairing and development support, improvements to Mobile Device Management, and more.
The seventh beta of tvOS 11 most likely focuses primarily on bug fixes and other small refinements, as the first six betas did. Apple's new tvOS 11 update is available for both registered developers and public beta testers. It will see a public release later this year.
Update: Today's update appears to include HDR assets for "J105a," the code name for a next-generation Apple TV capable of supporting a 4K resolution. References to J105a have previously been found in the HomePod firmware, suggesting we could perhaps see a release of a new Apple TV in the near future.
tvOS 11 Beta 7 contains some HDR assets for model J105A 😇 pic.twitter.com/IH2XdDfrrW— Guilherme Rambo (@_inside) August 21, 2017
Update 2: Apple has also released a new public beta of tvOS 11 for public beta testers.