watchOS 5.1 (build 16R591) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2018-10-30T17:21:29Z. The update package is 779.4 MB. This is a delta (partial) update that requires 4.3.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 68da5d219d124c3f13b8d33008ec1748e7147ce4.zip.