Apple today released the first software update for tvOS, taking the 4th-generation Apple tv to version 9.0.1. Apple didn't supply release notes for the update, so it's unknown for sure what was in it. Generally early updates of this type include "bug fixes and performance enhancements."
If you're not thrilled about installing the software update because of how long it used to take the first-though-third generation Apple TVs -- which didn't run tvOS -- to update, take heart. Users are reporting that the entire process takes less than five minutes.
Just open Settings on the Apple TV and the update is available for download and installation. The next "point release" of tvOS is expected soon, as tvOS 9.1 has been released in beta form to registered developers.