watchOS 4.2 (build 15S5100a) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2017-11-13T18:04:28Z. The update package is 178.94 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: 52d3ea7c49b0f0f6467a5e0eaf6cfc74e14d316e.zip.