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 491.39 MB. This is a delta (partial) update that requires 5.1.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: edc3cc27a0891d79e0c03bd4bb19a03955e58047.zip.