watchOS 5.1 (build 16R6591) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2018-10-30T17:21:07Z. The update package is 392.62 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: db355ed81edba1c1bb7eb6ff488f9d81fbdf362d.zip.