watchOS 4.2 (build 15S102) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2017-12-05T18:01:37Z. The update package is 599.02 MB. This is a delta (partial) update that requires 3.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: aa0b9cddd9d7dd8f3ba654c2eec47ffad349e427.zip.