watchOS 4.3.1 (build 15T6567) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2018-05-29T17:09:28Z. The update package is 65.27 MB. This is a delta (partial) update that requires 4.3.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 31cec6957a8ef6a6d0c6c7a43a4b9c25171def8e.zip.