watchOS 4.2 (build 15S5102) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2017-12-05T18:02:01Z. The update package is 106.87 MB. This is a delta (partial) update that requires 4.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: eba009e706fe56e38537e0748bc5a657a9932915.zip.