watchOS 4.3.1 (build 15T5535b) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2018-04-02T17:13:43Z. The update package is 148.46 MB. This is a delta (partial) update that requires 4.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: d98690f0d5ad6a7c809118cbb8549802a69076ce.zip.