watchOS 4.2 (build 15S102) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2017-12-05T18:01:52Z. The update package is 342.04 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: e4780df91d87f055ff3856df28ad8c30d6585ecc.zip.