It's not a DIN standard radio.
It's what GM calls their new silverbox radio and integrated center stack (ICS). The new CTS introduced this idea.
The actual radio receiver hardware is just a featureless silver box buried inside the dashboard. The ICS is the actual control panel on the outside and communicates with the radio over the vehicle's data bus. The center stack panel includes the climate controls and any other controls GM wants to integrate into the center stack.
In other words, it's going to be nearly impossible to upgrade.