watchOS 5.1 (build 16R591) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2018-10-30T17:21:34Z. The update package is 763.8 MB. This is a delta (partial) update that requires 4.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: bdf6c5aebb50b9ec78a910e9a619a1d41bd7a450.zip.