watchOS 5.2.1 (build 16U5101c) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2019-04-22T17:13:00Z. The update package is 495.98 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: 308c86a72d8141c10f14793e1868ccea96c5577c.zip.