watchOS 4.2.3 (build 15S6600b) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2018-02-19T21:17:45Z. The update package is 72.3 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: d719115c9d04ae809df7494ddd8b805a2aa1eab2.zip.