watchOS 4.3.1 (build 15T5535b) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2018-04-02T17:13:38Z. The update package is 346.01 MB. This is a delta (partial) update that requires 4.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 19a1ac202776e5eeed5c8db0e5fa726aa4bebbb5.zip.