watchOS 5.2.1 (build 16U5101c) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2019-04-22T17:12:55Z. The update package is 447.63 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: 04e46cdc3de7211eb064edcc2c674a1c2e20cc04.zip.