watchOS 9.0 (build 13S428) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2015-10-21T17:58:30Z. The update package is 519.04 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: 45a8531bdb3aca2014da18b92d1aa0698719c481.zip.