watchOS 4.3 (build 15T5199f) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2018-03-07T02:04:18Z. The update package is 306.43 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: 53ccb7b93fab053dc4791ff0dced4f0872c0ab00.zip.