watchOS 5.1 (build 16R6591) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm), released on 2018-10-30T17:21:52Z. The update package is 151.04 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: a6ef14ef282a54e54c90a73f064ce11146206219.zip.