watchOS 5.1.3 (build 16S535) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm, LTE), released on 2019-01-22T18:14:00Z. The update package is 211.66 MB. This is a delta (partial) update that requires 5.0.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: f3a3d4fa0674de597e2993cca7b4121713630bd0.zip.