watchOS 5.1 (build 16R5559d) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2018-09-18T17:23:01Z. The update package is 606.84 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: d4e52d00bb4d5173236fed734d40777b8c1230bd.zip.