watchOS 5.1 (build 16R5559d) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2018-09-18T17:22:45Z. The update package is 726.98 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: 73fb8c561625b2a2d2896de9cff71045c28ae582.zip.