This presentation reports the numerical simulations we have done in order to evaluate the performance of the first-light AO system of LBT. The simulation tool used for this purpose is the Software Package CAOS, applicable for a wide range of AO systems and for which a brief recall of the main features is made. The whole process of atmospheric propagation of light, wavefront sensing (using a complete model of the pyramid wavefront sensor), wavefront reconstruction using the LBT672 adaptive secondary mirror modes), and closing of the loop, is simulated. The results are given in terms of obtained Strehl ratios in J-, H-, and K-band. Estimation of the resulting sky-coverage in K-band for different regions of the sky are also expressed. A comparison with the performance that would be obtained by using a Shack-Hartmann sensor is presented, confirming the gain achievable with the pyramid sensor.