watchOS 4.2 (build 15S5100a) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2017-11-13T18:04:17Z. The update package is 200.08 MB. This is a delta (partial) update that requires 4.0 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: f23c278ed030f6717f41fa1a1ef30f9b310bbc78.zip.