tvOS 11.3 (build 15L211) is an official Apple over-the-air update for the Apple TV 4 (2015), released on 2018-03-29T17:05:09Z. The update package is 988.4 MB. This is a delta (partial) update that requires 9.0.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 2e677566446d89ae1b729566f343581fe2f87a6b.zip.