watchOS 4.2 (build 15S102) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2017-12-05T18:02:00Z. The update package is 213.44 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: 7f0fd3f52b28a3963bf7ebe13cf11659c59f5d7b.zip.