tvOS 12.1.1 (build 16K45) is an official Apple over-the-air update for the Apple TV 4 (2015), released on 2018-12-05T18:08:53Z. The update package is 984.23 MB. This is a delta (partial) update that requires 10.0.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 1094e088fbd77aa6ff8ce965c24cbdc29ee9a559.zip.