watchOS 5.1 (build 16R5584a) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2018-10-15T17:09:38Z. The update package is 732.99 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: 7e1c20980486e29f7d3d1e4058c6c863b75368a7.zip.