watchOS 4.3.1 (build 15T5545b) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2018-04-16T17:04:42Z. The update package is 346.03 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: 44fb1f887279568cf750ed69a794e553f24be71c.zip.