watchOS 5.1 (build 16R591) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2018-10-30T17:21:03Z. The update package is 771.29 MB. This is a delta (partial) update that requires 4.0 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: d6b72a7dd5704bb476e3386e4c24e6be2dc5af37.zip.