watchOS 4.2 (build 15S102) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2017-12-05T18:01:51Z. The update package is 571.3 MB. This is a delta (partial) update that requires 3.2.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 923bd9374f77bcd905a0d2c5770a39e91288725b.zip.