watchOS 5.2.1 (build 16U5091b) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2019-04-08T17:12:37Z. The update package is 443.17 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: 456214c2b200f075c3f174951591be542d44be04.zip.