watchOS 5.1 (build 16R6591) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2018-10-30T17:21:33Z. The update package is 434.1 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: a4f402fd3d531637c35503d542a3d16f8f76a88d.zip.