watchOS 4.3 (build 15T212) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-03-29T17:09:11Z. The update package is 374.96 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: a0c2ea646e2f123f3554d0b4b47d33344d47019a.zip.