watchOS 5.2.1 (build 16U5113a) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm), released on 2019-05-07T17:19:37Z. The update package is 471.34 MB. This is a delta (partial) update that requires 5.1.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: e4530ce74368c132c83d1f64ee4fc4fa2a7a2488.zip.