I2C and 5v slave

Is it possible to interface a 5volt slave device on the I2C bus of the 811 Eval. board directly or do should an approprite bidirectional level shifter be used ?

I understand that the 811 pins are 5 volts tolerant, however I am worried about the OLED.

According to the I2C spec the I2C lines are not driven high, except by the external pull up resistors, but I am not too sure.

TIA.