tvOS 12.1.2 (build 16K5532a) is an official Apple over-the-air update for the Apple TV 4 (2015), released on 2018-12-19T18:20:47Z. The update package is 66.75 MB. This is a delta (partial) update that requires 12.1.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: f76d5111c31db3edc8b937edddda52d3cb690b32.zip.