watchOS 5.1 (build 16R5568d) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2018-10-02T17:14:28Z. The update package is 389.25 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: 350b3624721bc5b44f9a602874479dba48f46a90.zip.