watchOS 5.1.3 (build 16S535) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2019-01-22T18:12:25Z. The update package is 148.44 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: aa725d3dd7659f7f9d8a0fadc4070cc5dbde2c3e.zip.