watchOS 4.3 (build 15T212) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2018-03-29T17:07:28Z. The update package is 307.64 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: a30f4d582df72b05355d65841717c25b919d8787.zip.