watchOS 5.1 (build 16R6591) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2018-10-30T17:21:06Z. The update package is 577.97 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: 7fdb971560304cc799f6026e8eaf914bfff52459.zip.