watchOS 9.0 (build 15T212) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2018-03-29T17:07:18Z. The update package is 1001.61 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: 4aa1f7e0b6475462246a6c07a8a3715fd5588892.zip.