watchOS 5.1.3 (build 16S535) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2019-01-22T18:11:48Z. The update package is 797.29 MB. This is a delta (partial) update that requires 4.2.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 2b505b45bbf6c536e485e54a81bf5b0d8675db72.zip.