watchOS 5.1.2 (build 16S46) is an official Apple over-the-air update for the Apple Watch Series 4 (40mm, LTE), released on 2018-12-06T18:04:54Z. The update package is 209.49 MB. This is a delta (partial) update that requires 5.0 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 240aec6f0921fdfa59cf455cf775b5d6ea355001.zip.