watchOS 5.2.1 (build 16U5091b) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm), released on 2019-04-08T17:13:16Z. The update package is 442.4 MB. This is a delta (partial) update that requires 5.1.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: ab43929ea3737c0753c9d20fb2ba0bcf1a35ca99.zip.