watchOS 5.1.3 (build 16S535) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2019-01-22T18:12:27Z. The update package is 76.12 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: c44d6c40ab5a46c29a8380c9e2eb797f454d782d.zip.