watchOS 5.1.3 (build 16S6535) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2019-01-22T18:11:44Z. The update package is 82.16 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: ca1e7791af6fab83481256ed44638aba9c457179.zip.