watchOS 5.1 (build 16R591) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-10-30T17:21:18Z. The update package is 793.4 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: b44aa394ea6ddbe8e99959727fc2f8032ab0fd92.zip.