iOS 12.3 (build 16F5129d) is an official Apple over-the-air update for the iPhone XS, released on 2019-04-08T17:05:03Z. The update package is 334.93 MB. This is a delta (partial) update that requires 12.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 48f9ef8951c27359b973caa1c0c1dd2ba4f48eed.zip.