watchOS 5.0 (build 16R364) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-09-12T19:18:53Z. The update package is 809.21 MB. This is a delta (partial) update that requires 4.0.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: b5d636bc1ba1fe3bc1a0c3117792c113d815ec51.zip.