watchOS 5.2.1 (build 16U5113a) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm, LTE), released on 2019-05-07T17:19:50Z. The update package is 492.73 MB. This is a delta (partial) update that requires 5.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 40af4b6d5918f33c08c83c5c1b86aec7c6336e8b.zip.