watchOS 5.1 (build 16R591) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2018-10-30T17:21:05Z. The update package is 132.64 MB. This is a delta (partial) update that requires 5.0.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 2f4ef5f8cbd45ea7bb931050278992e925c6c635.zip.