watchOS 5.2.1 (build 16U5101c) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm), released on 2019-04-22T17:13:27Z. The update package is 451.41 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: 6ca40325457a23ff399d88b867080357d5668326.zip.