watchOS 5.1.3 (build 16S5535a) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2019-01-07T18:16:24Z. The update package is 175.58 MB. This is a delta (partial) update that requires 5.0 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 9ef44c1185f4d353f7b64e03565d888a5f090d41.zip.