watchOS 4.0 (build 15R372) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2017-09-12T19:04:48Z. The update package is 778.42 MB. This is a delta (partial) update that requires 2.2.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 67ca0d1637995091d0a44df64ba1ad5c7cf0d0bb.zip.