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 saw little screen time at today's event, and in fact, it wasn't even officially announced on stage. The new operating system was largely glossed over, with the exception of an announcement for an upcoming Amazon Prime Video app.
According to Apple's release notes, tvOS 11 brings automatic light/dark appearance switching, Home screen syncing options, new background modes and notification support, Focus API improvements, custom sound support, network-based pairing and development support, and improvements to Mobile Device Management.
tvOS 11 is only available for registered developers at the current point in time, but Apple's beta site now includes tvOS 11, suggesting a public tvOS beta is coming.