watchOS 4.3.1 (build 15T567) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2018-05-29T17:09:14Z. The update package is 695.84 MB. This is a delta (partial) update that requires 3.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: afa35e71bd9d39e8a2a677f1b32ac5c9c9af3776.zip.