watchOS 5.1 (build 16R591) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm), released on 2018-10-30T17:21:51Z. The update package is 159.21 MB. This is a delta (partial) update that requires 5.0.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 5f86dd4d284877a96358d398982364bc65354b3f.zip.