watchOS 4.0 (build 15R372) is an official Apple over-the-air update for the Apple Watch Series 2 (42mm), released on 2017-09-12T19:05:07Z. The update package is 556.61 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: 67a3ccb564ac516dea54b41e2fdf90f4a5faaadc.zip.