watchOS 5.1 (build 16R591) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2018-10-30T17:21:04Z. The update package is 732.57 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: 63f9113e21fc200a87dda7f940ea7e84cb6e11db.zip.