watchOS 5.1 (build 16R5584a) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-10-15T17:09:50Z. The update package is 432.49 MB. This is a delta (partial) update that requires 5.0 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 49134862ea234f21be4bbf7e519a6bf0d6c04de7.zip.