watchOS 4.3.1 (build 15T5565a) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2018-05-07T17:22:57Z. The update package is 82.77 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: 3cdb7357524f477677474b63c732c8c1eb034b5a.zip.