watchOS 4.3 (build 15T5187e) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2018-02-21T18:12:20Z. The update package is 342.3 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: 2e1423361095ab7d9628edce43a28fc84426f98e.zip.