watchOS 4.0 (build 15R5371a) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2017-08-28T16:53:19Z. The update package is 187.16 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: 091aa3e3804f889ff445c4cf6b17d8fda9a3b712.zip.