tvOS 13.3 (build 17K449) is an official Apple over-the-air update for the Apple TV 4 (2015), released on 2019-12-10T18:33:09Z. The update package is 845.42 MB. This is a delta (partial) update that requires 12.4 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 9081f4bc3459e032be14e4ca9737cb2a171ef368.zip.