watchOS 5.2.1 (build 16U6113) is an official Apple over-the-air update for the Apple Watch Series 4 (40mm, LTE), released on 2019-05-13T17:18:04Z. The update package is 122.98 MB. This is a delta (partial) update that requires 5.2.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 331b674b6df52a39392bb8a26c363b22c93b6385.zip.