watchOS 4.3 (build 15T5212a) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-03-16T20:09:31Z. The update package is 399.51 MB. This is a delta (partial) update that requires 4.0 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 9bc21525ae1e1b97c552a555d012a626109e37bc.zip.