The tvOS 12 public beta can be obtained by going to the Settings app on the Apple TV and navigating to the Software Updates section under "System." "Get Public Beta Updates" will need to be toggled on, and once it is, the Apple TV will download the beta software.
tvOS 12 introduces long-awaited support for Dolby Atmos, and when tvOS 12 launches this fall, iTunes will be home to the largest collection of Dolby Atmos-supported movies. As with the launch of 4K HDR, previously purchased content will be upgraded to include Dolby Atmos on all supported titles at no cost.
tvOS 12 features a zero sign-on option that lets cable subscribers watch live channels and on-demand programs they're entitled to through their cable subscription simply by being logged into their home internet networks. This feature will be limited to Charter Spectrum users to begin with, but Apple plans to expand it to additional providers in the future.
Other tvOS 12 features include the ability to autofill passwords from the iPhone to sign into Apple TV apps more quickly, and support for Home Control systems like Crestron and Savant, which will be able to be used to control the Apple TV.
Apple has also made the Apple TV Remote a default option in Control Center on iOS devices with the iOS 12 beta, there are new aerial screensavers created with help from the International Space Station, and aerial screensavers now offer up location information, a feature that's activated in this beta.
tvOS 12 will see a public launch this fall, and until that time, will be limited to developers and public beta testers as Apple works out bugs and other issues.