watchOS 5.1.3 (build 16S535) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2019-01-22T18:12:16Z. The update package is 764.8 MB. This is a delta (partial) update that requires 4.2.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: cdd1a370c89ec3bd599fce941e4d867a98bf4f9f.zip.