watchOS 5.1 (build 16R5589c) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2018-10-22T17:19:06Z. The update package is 733.19 MB. This is a delta (partial) update that requires 4.3.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: a3626ba51646088f6353437cf6ebe8e0abb93ca9.zip.