watchOS 5.1 (build 16R5584a) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2018-10-15T17:09:33Z. The update package is 551.48 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: 5c414732aa81fbd95f73920cfe96fc5db4301fe7.zip.