watchOS 4.2 (build 15S5100a) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2017-11-13T18:04:27Z. The update package is 215.09 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: 4360e9bb3904bda2a6f5b19c5061ca226f3d7553.zip.