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 538.02 MB. This is a delta (partial) update that requires 3.2.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: ec0194da8add7cdcc2f009bbf68a4c378b863096.zip.