watchOS 4.2.3 (build 15S600b) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2018-02-19T21:17:40Z. The update package is 572.6 MB. This is a delta (partial) update that requires 3.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 42055fb8add5b215aa456daabfee8419140e7618.zip.