watchOS 4.0 (build 15R5372) is an official Apple over-the-air update for the Apple Watch (38mm), released on 2017-09-12T19:05:12Z. The update package is 250.11 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: ca958fc8b3e68377580ddbed5929b5395d7cea2c.zip.