watchOS 4.0 (build 15R5372) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2017-09-12T19:05:13Z. The update package is 105.38 MB. This is a delta (partial) update that requires 4.0 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: f8cf33dadab23a333fe01a84b91d101ba8ef37d4.zip.