watchOS 5.1 (build 16R5589c) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm), released on 2018-10-22T17:19:58Z. The update package is 107.34 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: a13f9561870348a9f36956d09b7923f4a94fb185.zip.