watchOS 4.2 (build 15S102) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2017-12-05T18:01:41Z. The update package is 272.68 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: b64b0a5358a46c53229e418a9226a4214d56d8ca.zip.