watchOS 5.1.3 (build 16S5531a) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm), released on 2018-12-19T21:06:30Z. The update package is 81.02 MB. This is a delta (partial) update that requires 5.1.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: f55d353e7eddf8407971f22341657b82f6a97c1b.zip.