watchOS 4.0 (build 15R5372) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2017-09-12T19:05:32Z. The update package is 89.11 MB. This is a delta (partial) update that requires 4.0 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: ab59803bac9df79c1eb965e6c0371eb897b6e7d3.zip.