watchOS 5.2.1 (build 16U5091b) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm), released on 2019-04-08T17:13:20Z. The update package is 154 MB. This is a delta (partial) update that requires 5.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: c49a29851175de977f0a388dc9f77a59f36ce52f.zip.