watchOS 5.1 (build 16R5584a) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2018-10-15T17:10:04Z. The update package is 748.08 MB. This is a delta (partial) update that requires 4.3.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: f9c26b88e6684004cb95ffb23b304233310f0943.zip.