watchOS 4.3 (build 15T5209a) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2018-03-12T20:07:04Z. The update package is 306.54 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: c6d1eec7ad82768a94c57dc06f97eca301937769.zip.