watchOS 4.0 (build 15R372) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2017-09-12T19:04:49Z. The update package is 580.58 MB. This is a delta (partial) update that requires 3.1.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 903dab9bbedca4d5355fccb17ef48b520ac7f4c9.zip.