watchOS 5.1.2 (build 16S46) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2018-12-06T18:04:28Z. The update package is 820.97 MB. This is a delta (partial) update that requires 4.0.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: f6ab71a9b593a37de1407ba2662a9d878920a37f.zip.