watchOS 4.3 (build 15T5176c) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2018-02-07T18:09:47Z. The update package is 305.76 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: acce9f081d76dc2cfcc2f6c249cdd6722a96af2f.zip.