watchOS 4.3 (build 15T5187e) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2018-02-21T18:12:13Z. The update package is 386.09 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: 8e156c761b682b034397b920aefc7541bc46afb9.zip.