watchOS 5.2.1 (build 16U5110a) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2019-04-29T17:39:00Z. The update package is 98.72 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: 7295b9ab0fef494f71d659dd020985cea8a2a9ca.zip.