watchOS 4.3.1 (build 15T567) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2018-05-29T17:09:38Z. The update package is 370.74 MB. This is a delta (partial) update that requires 4.2.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: c87754e25011b9db959d93cd1a11305cabd2f5cb.zip.