watchOS 5.1.2 (build 16S46) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-12-06T18:04:23Z. The update package is 628.78 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: fd5d15c9f4df1a92c31119981d6eba45139e61c8.zip.