watchOS 4.0 (build 15R5372) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2017-09-12T19:05:12Z. The update package is 297.47 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: acb1c98550090ad73bd158f52e464102870b9423.zip.