watchOS 5.3 (build 16U5545c) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2019-06-11T17:13:38Z. The update package is 151.06 MB. This is a delta (partial) update that requires 5.2.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 7cb13e85da728206c3060a0b894074a054b598a8.zip.