watchOS 5.1 (build 16R5584a) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2018-10-15T17:09:53Z. The update package is 778.71 MB. This is a delta (partial) update that requires 4.3.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: b3050ba01b3b83e5eb92bfb3c9935b86bb365246.zip.