watchOS 5.2.1 (build 16U5091b) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm, LTE), released on 2019-04-08T17:13:39Z. The update package is 108.95 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: 1cf3bf312948f00bb05261bbc252fa07cbe664d2.zip.