tvOS 11.3 (build 15L5211b) is an official Apple over-the-air update for the Apple TV 4 (2015), released on 2018-03-20T20:02:28Z. The update package is 23 MB. This is a delta (partial) update that requires 11.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 7eafd7552e46ea5e9c424e48f31f18a2ffe827b5.zip.