watchOS 5.3 (build 16U5545c) is an official Apple over-the-air update for the Apple Watch Series 4 (40mm, LTE), released on 2019-06-11T17:14:13Z. The update package is 474.77 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: 4d2397570acb1908cae5a98a1f4d5fbd413389bd.zip.