How does the new CIP differ from the CEP?

The CEP did not allow for modeling of diurnal and subdiurnal nutation periods. The CIP is an intermediate pole separating, by convention, the motion of the pole of the ITRS in the GCRS by dividing nutation from polar motion explicitly at the 2-day nutation period. Nutations with periods less than two days are modeled by their equivalent polar motion.