watchOS 5.1.3 (build 16S535) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2019-01-22T18:11:52Z. The update package is 214.6 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: 4ff3c0f176e28e0bff58021840f5f716d18cf0c1.zip.