watchOS 4.0 (build 15R372) is an official Apple over-the-air update for the Apple Watch (38mm), released on 2017-09-12T19:04:47Z. The update package is 764.36 MB. This is a delta (partial) update that requires 2.2.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: ac495f4c9321de2035fa06fca09aadf10d2a5e34.zip.