watchOS 4.3.1 (build 15T5555c) is an official Apple over-the-air update for the Apple Watch Series 2 (42mm), released on 2018-05-01T17:06:42Z. The update package is 326.63 MB. This is a delta (partial) update that requires 4.2.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 1466eb096a1e88ea0cec89efd138a8ff07f2291a.zip.