watchOS 5.1 (build 16R5568d) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2018-10-02T17:14:23Z. The update package is 733.6 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: 276e186226b17090b5a9e1e01533f5139cfe2c7a.zip.