watchOS 4.3.1 (build 15T5555c) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-05-01T17:06:56Z. The update package is 375.98 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: e0e3cab9972fa42159416cd5196b3402dd06748e.zip.