watchOS 5.2.1 (build 16U5091b) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2019-04-08T17:12:40Z. The update package is 507.45 MB. This is a delta (partial) update that requires 5.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 91b99595e4d72b5fa61824db72fa1c22476ef3ef.zip.