watchOS 4.3 (build 15T5165e) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2018-01-25T18:04:02Z. The update package is 287.98 MB. This is a delta (partial) update that requires 4.2.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 434f632d48cb1eece0934437cade8ce09478058e.zip.