watchOS 4.0 (build 15R372) is an official Apple over-the-air update for the Apple Watch Series 2 (38mm), released on 2017-09-12T19:05:02Z. The update package is 539.56 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: ff3787ae0c992920678d7d3775190404432a695b.zip.