The fourth beta of tvOS 10 has now been seeded to developers. This update comes two weeks after the third release. With this beta specifically we just find bug fixes and stability improvements. Other than that, there are no UI changes like we saw with iOS 10.
tvOS 10, specifically, includes a new dark mode, single sign-on with TV service providers, and a new remote app for iOS.
To get this update developers can download it from Settings. If you don’t have it yet, you can download it from the Apple Developer Center.