watchOS 4.0 (build 15R5372) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2017-09-12T19:05:30Z. The update package is 218.61 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: 569464e0bb1941d6019cb057b30c5e33b49a74a7.zip.