watchOS 5.3 (build 16U5558b) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm, LTE), released on 2019-06-24T17:25:41Z. The update package is 476.57 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: 05f16cedb06424b684b5432c51cb158d17eabe9c.zip.