watchOS 4.3 (build 15T5176c) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2018-02-07T18:09:46Z. The update package is 305.8 MB. This is a delta (partial) update that requires 4.2.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 8151c00915edd0dec47d366c9f235a0d6249a30e.zip.