tri-state / high-z / high impedance output with gpio input
Looks like an open drain output pin.  So you need a pull-up of some sort.  If you want to utilize an internal pull-up, that will probably get the job done just fine and save you some board area, just make sure it's initialized correctly before using the value read from the pin.  It's perfectly fine to pull it up to any voltage within the allowed range for both chips.  Lower voltages will generally work fine, higher voltages may or may not be OK depending on how the output pin is designed.  You should be fine with a pull-up to 3.3 volts.