watchOS 4.3 (build 15T5212a) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2018-03-16T20:09:26Z. The update package is 324.53 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: 1064d7390caeddbb47c74e791d863a1d05c1e007.zip.