watchOS 5.1.3 (build 16S5523a) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2018-12-10T18:10:10Z. The update package is 175.79 MB. This is a delta (partial) update that requires 5.0.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 9fa4cc5e6f551a8929f786df2508187e9d582b2b.zip.