watchOS 4.3.1 (build 15T5565a) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2018-05-07T17:23:41Z. The update package is 333.18 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: bf05a9098a942c9a917fc0fbe4879c43baeebee1.zip.