Registered developers can download tvOS 11 by connecting the Apple TV to a computer with a USB-C cable and installing the beta software using iTunes.
tvOS 11 received little attention at the Worldwide Developers Conference, but according to Apple's release notes, it introduces a few new features to the operating system, and the third beta likely focuses on bug fixes, as the second beta did.
tvOS 11 introduces 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 new tvOS 11 update is available for registered developers and for the first time, public beta testers. A new tvOS 11 beta for public beta testers is likely to come out later this week.