watchOS 4.3 (build 15T212) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2018-03-29T17:09:40Z. The update package is 331.87 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: a1fb422fa672bb06cecfac6da88bf857f20d700d.zip.