watchOS 4.3.1 (build 15T567) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2018-05-29T17:09:15Z. The update package is 696.78 MB. This is a delta (partial) update that requires 3.1.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 9132add47eb3edd02c049cab3ae35a6cc99252f1.zip.