watchOS 5.1.3 (build 16S535) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2019-01-22T18:11:38Z. The update package is 174.44 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: 63329319b305786dfe0fb9ec6ea85407dd510d10.zip.