watchOS 4.0 (build 15R5372) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2017-09-12T19:05:26Z. The update package is 92.22 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: 956513e62b2de9d541e0f01a39094d469ad630f3.zip.