watchOS 5.1.3 (build 16S6535) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2019-01-22T18:12:30Z. The update package is 96.65 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: 490e85812bef851ae12c51228208579ca78589d2.zip.