watchOS 4.2.3 (build 15S6600b) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2018-02-19T21:17:17Z. The update package is 66.66 MB. This is a delta (partial) update that requires 4.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: e78afdbba84ee3b828ac8f920f7564d2631c8517.zip.