Designed for the fourth and fifth-generation Apple TV models, the new tvOS 12.4 developer beta can be downloaded onto the Apple TV through a profile that's installed using Apple's Xcode software.
tvOS updates have historically been minor in scale, focusing on under-the-hood bug fixes and improvements rather than major outward-facing changes. Apple provides little to no information on what's included in tvOS updates, so we may not discover anything new after installing the new beta.
We don't always know what's new, but we do share tvOS updates so developers are able to download new software upon release.
tvOS 12.3, the prior update, was a one of the most significant tvOS updates we've had to date, introducing an updated TV app along with a new Channels feature designed to let Apple TV users purchase subscriptions to services like HBO, Showtime, Starz, and more right in the TV app.
Should we discover new features in tvOS 12.4, we'll update this post with details.