watchOS 4.2 (build 15S5100a) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2017-11-13T18:04:40Z. The update package is 79.41 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: 89e4f3786282f6806b688260f243760064ba837e.zip.