watchOS 4.2.3 (build 15S600b) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2018-02-19T21:17:40Z. The update package is 614.36 MB. This is a delta (partial) update that requires 3.1.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: b7eb0fdf4229bf2d54e0ec182f1bf32377806a8a.zip.