  We derive the rest-frame $K$-band luminosity function for galaxies in 32
clusters at $0.6 < z < 1.3$ using deep $3.6\mu$m and $4.5\mu$m imaging from the
Spitzer Space Telescope InfraRed Array Camera (IRAC). The luminosity functions
approximate the stellar mass function of the cluster galaxies. Their dependence
on redshift indicates that massive cluster galaxies (to the characteristic
luminosity $M^*_K$) are fully assembled at least at $z \sim 1.3$ and that
little significant accretion takes place at later times. The existence of
massive, highly evolved galaxies at these epochs is likely to represent a
significant challenge to theories of hierarchical structure formation where
such objects are formed by the late accretion of spheroidal systems at $z < 1$.
