watchOS 4.3 (build 15T5199f) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2018-03-06T18:07:50Z. The update package is 306.53 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: f4c4f64cb8c58081fc13eee64abadc2d9a0fb72e.zip.