watchOS 4.3 (build 15T5209a) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2018-03-12T20:07:55Z. The update package is 331.32 MB. This is a delta (partial) update that requires 4.2.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 94b99985cc7f09e24d59ad6f2021690a2d286d3e.zip.