watchOS 5.1.3 (build 16S535) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm), released on 2019-01-22T18:13:37Z. The update package is 146.28 MB. This is a delta (partial) update that requires 5.1.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 527020af2359c3e9d7fb2c0588532934baa2bbca.zip.