watchOS 5.3 (build 16U5537b) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2019-05-28T17:12:33Z. The update package is 222.33 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: 27692402d77788e7098a89ec3f4ffa0202c23ff8.zip.