tvOS 13.3.1 (build 17K795) is an official Apple over-the-air update for the Apple TV 4 (2015), released on 2020-01-28T18:42:31Z. The update package is 845.99 MB. This is a delta (partial) update that requires 12.2.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 304655b3b15254645d7171d984aa924919511099.zip.