watchOS 4.2.3 (build 15S600b) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2018-02-19T21:17:15Z. The update package is 597.15 MB. This is a delta (partial) update that requires 3.1.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 7998b2c2a82c127289e78f4ea524c3fadcef8d94.zip.