watchOS 4.3 (build 15T5209a) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2018-03-12T20:07:42Z. The update package is 360.77 MB. This is a delta (partial) update that requires 4.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: b1c0d5db29e8ee7501c738abc4d4f68114ff3da7.zip.