watchOS 5.1.2 (build 16S46) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-12-06T18:04:22Z. The update package is 796.93 MB. This is a delta (partial) update that requires 4.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 8afaac0eb2588e1c9a5ee7b5f88284bf5def28de.zip.