Aside from releasing third betas of iOS 11 and macOS High Sierra, Apple today also seeded tvOS 11 beta 3 (build number 15J5324f) for the fourth-generation Apple TV to its registered developers and members of the paid Apple Developer Program.
No new outward-facing user features have been added in beta 3.
Non-developers can test tvOS 11 betas by signing up for Apple’s Beta Software Program at beta.apple.com. Be sure to sign up through your computer using the same Apple ID you use for iCloud services on your devices, then go to Settings → System → Software Updates on your Apple TV and enable the feature labeled Get Beta Updates.
The Software Update mechanism on your Apple TV will now put up a prompt when a new tvOS 11 beta is available for download.
tvOS 11 includes minor features like the ability to synchronize your Home screen layout across multiple Apple TVs via iCloud, automatic switching between Light and Dark mode based on local time, new background multitasking modes, notification support, custom sound support, layered image improvements, right-to-left language support and other tidbits.