watchOS 5.1 (build 16R5589c) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm), released on 2018-10-22T17:19:59Z. The update package is 49.48 MB. This is a delta (partial) update that requires 5.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: a217e535d1bf4cfa5c7c3d1dccb123dbd3d2a9c3.zip.