watchOS 4.2 (build 15S102) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2017-12-05T18:00:45Z. The update package is 790.71 MB. This is a delta (partial) update that requires 2.2.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 3e4cf731a8bb1f0ab3c490d890729f9d8bfde3ba.zip.