watchOS 4.2 (build 15S5102b) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2017-11-17T18:17:58Z. The update package is 152.09 MB. This is a delta (partial) update that requires 4.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: beb812b43070fa753a1eeb8992492d1d7b812b57.zip.