watchOS 4.3.1 (build 15T567) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-05-29T17:09:29Z. The update package is 370.9 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: 2de6effa85b4199d9b07e3f2005596ec2c30c77b.zip.