watchOS 4.2.3 (build 15S600b) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2018-02-19T21:17:56Z. The update package is 167.2 MB. This is a delta (partial) update that requires 4.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 6267c0bb993dd0cab6b598918d07e32ec057a9a3.zip.