watchOS 4.3.1 (build 15T6567) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2018-05-29T17:09:41Z. The update package is 122.6 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: 9eb33acdcb50cbdf5456918fe26eff0bf47d1598.zip.