watchOS 4.3 (build 15T5212a) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2018-03-16T20:09:47Z. The update package is 331.42 MB. This is a delta (partial) update that requires 4.2.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: c8afaa138abd6541b92ff5b94e7f1ec4fec89d7e.zip.