The K26 SOM supports all I/O standards supported by the respective bank that a signal is connected to with the exception of I/O standards that require a reference voltage (VREF). For more information, refer to the UltraScale Architecture SelectIO Resources User Guide (UG571).
During power-up and configuration, internal pull-up resistors are disabled and each SelectIO™ pin is set to 3-state.
The K26 SOM is built with the XCK26-SFVC784-2LV device; which has a -2 speed grade and is an LV device (operates at VCCINT = 0.72V). Consult the corresponding I/O speed tables in Zynq UltraScale+ MPSoC Data Sheet: DC and AC Switching Characteristics (DS925) for the definition of maximum data rates.