watchOS 4.2 (build 15S5102b) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2017-11-17T18:17:57Z. The update package is 89.17 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: 1dbc8afe8709bd9cf9f7eb1e2fa4a3b4cb9a78d9.zip.