watchOS 5.1 (build 16R5568d) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2018-10-02T17:14:33Z. The update package is 575.64 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: e25c8085243e0f0b0a3d01b797a330af555f994f.zip.