watchOS 5.1.3 (build 16S535) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2019-01-22T18:11:53Z. The update package is 185.15 MB. This is a delta (partial) update that requires 5.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 0dc30334f7f66deefabc0f44c1f9dfe62b20610c.zip.