watchOS 5.2.1 (build 16U5091b) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2019-04-08T17:12:33Z. The update package is 443.42 MB. This is a delta (partial) update that requires 5.1.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: aabef8ff762e446c31ce9f6ff1fdc527bd69bab7.zip.