watchOS 4.2 (build 15S102) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2017-12-05T18:00:56Z. The update package is 175.34 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: d9488b414360f18a8b4970ea53093a78078a3121.zip.