watchOS 5.1.3 (build 16S5523a) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2018-12-10T18:10:23Z. The update package is 190.14 MB. This is a delta (partial) update that requires 5.0 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 07a1184b910181ce5c22f65d98e0869d311dd06d.zip.