watchOS 4.2.3 (build 15S600b) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-02-19T21:17:48Z. The update package is 214.67 MB. This is a delta (partial) update that requires 4.0.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 9a08e807ce2f504573318ee6e0aeba373eda55bd.zip.