watchOS 5.1.3 (build 16S5535a) is an official Apple over-the-air update for the Apple Watch Series 4 (40mm), released on 2019-01-07T18:16:46Z. The update package is 76.34 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: 89860cb9aef9e5f4736f642efac5c16f363b1ad8.zip.