watchOS 4.2.3 (build 15S6600b) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-02-19T21:17:50Z. The update package is 69.07 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: 42fc2d141a6f3c8e1890fec6fa0fc0d64d1ee0c4.zip.