watchOS 4.3.1 (build 15T567) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-05-29T17:09:28Z. The update package is 408.38 MB. This is a delta (partial) update that requires 4.0 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 4174d367cc001051d3193bc46812cbafde536be8.zip.