watchOS 4.2.3 (build 15S6600b) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2018-02-19T21:17:16Z. The update package is 79.04 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: 7977e2ccf00d791c5a2d159852ad6a209164a510.zip.