Is XBEE actually programmable?

I have two XBEE Pros. I'm used to using them as serial portals, but I've been taking interest in the other 16 pins on the board. I have several projects that use XBEE with an arduino, and it would be great to cut out the middleman, the arduino.

I understand how to enable/disable GPIOs and whatnot, but is there an actual c file I can run a sketch on, something like arduino? Or is it all AT commands? Ideally I would like to upload an arduino-like sketch to the xbee to take incoming serial data and turn it into PPM on a GPIO. Yet, I can't find any place for code in XCTU. Is this possible?

Hope this helps.