watchOS 4.2 (build 15S5100a) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2017-11-13T18:03:58Z. The update package is 273.2 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: 26acde50f1329ce262c24ec8df9745f837ebe26c.zip.