watchOS 5.2.1 (build 16U5101c) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2019-04-22T17:13:08Z. The update package is 136.76 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: 2e49ecea84303999d584a8fe392cc5df15643662.zip.