watchOS 9.0 (build 15S542) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2018-01-19T18:08:01Z. The update package is 984.31 MB. This is a delta (partial) update that requires 8.2.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 4cea5a2d2fc27fb7e894d21379a81b9dc4cacd4a.zip.