watchOS 5.1 (build 16R5559d) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2018-09-18T17:23:07Z. The update package is 741.57 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: 77f3f69efc1bb381f7d956329d88ba062e797cbd.zip.