watchOS 4.2 (build 15S5102b) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2017-11-17T18:17:49Z. The update package is 179.22 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: 578c0a510c158805043025cfba1b3cce92158aca.zip.