Registered developers are able to download the tvOS 16.4 update by downloading a profile on the Apple TV using Xcode.
tvOS updates are typically minor in scale, focusing on internal bug fixes and improvements rather than notable outward-facing changes. There is no word as of yet what's included in the tvOS 16.4 update, but we'll update this article if we find anything new.
Apple shares some information on tvOS releases in its tvOS support document, which is updated after each tvOS launch, but it doesn't provide beta release notes.
