watchOS 5.1.3 (build 16S535) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm), released on 2019-01-22T18:13:29Z. The update package is 165.17 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: dde673a43922e70617c02cd36bd2dd3a2cf97e5b.zip.