watchOS 5.1 (build 16R6591) is an official Apple over-the-air update for the Apple Watch Series 2 (42mm), released on 2018-10-30T17:21:00Z. The update package is 393.54 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: c8ccb785e2f0b5485ee1451ceb29019fbe9b8fc5.zip.