iPadOS 12.3 (build 16F5156a) is an official Apple over-the-air update for the iPad Pro 3 (12.9-inch, Cellular), released on 2019-05-10T17:09:19Z. The update package is 473.61 MB. This is a delta (partial) update that requires 12.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 55b9d1dba56660bba8ad752cba6c66fefcff6f5d.zip.