watchOS 5.1.3 (build 16S6535) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm), released on 2019-01-22T18:13:45Z. The update package is 74.3 MB. This is a delta (partial) update that requires 5.1.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 73fbfcbb520f7f8e2658d6e1d1f7cad83f4f7e78.zip.