watchOS 5.2.1 (build 16U5091b) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2019-04-08T17:12:41Z. The update package is 149.58 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: 9c5bc536ae9088621dae97c0517cc5ee69602761.zip.