watchOS 4.2 (build 15S102) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2017-12-05T18:01:50Z. The update package is 614.12 MB. This is a delta (partial) update that requires 3.1.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: d44170d4b0b3e0e71a8ab40c526d587918d522e0.zip.