watchOS 5.2.1 (build 16U5113a) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm), released on 2019-05-07T17:19:38Z. The update package is 452.9 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: 315b97c6d692240db2a8d284c6e54abc281c1094.zip.