watchOS 4.3 (build 15T212) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm), released on 2018-03-29T17:10:02Z. The update package is 331.34 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: 6b046e1a20b3ca3f44703e851bb4699b7d3dbfd3.zip.