watchOS 4.0 (build 15R5371a) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2017-08-28T16:53:18Z. The update package is 527.73 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: 6ad7ea8ca63550a84c6135097f58ea3136a778d5.zip.