watchOS 5.2.1 (build 16U5110a) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm, LTE), released on 2019-04-29T17:39:59Z. The update package is 212.49 MB. This is a delta (partial) update that requires 5.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 728c0ec10bb17709111efd4130424994c867fedd.zip.