watchOS 5.1 (build 16R5577c) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm), released on 2018-10-09T17:12:27Z. The update package is 159.68 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: d687eca43c883641cea6b30426948123253f84ed.zip.