  We study the stellar mass content of massive haloes in the redshift range
0.86<z<1.34, by measuring: (1) The stellar mass in the central galaxy versus
total dynamical halo mass. (2) The total stellar mass (including satellites)
versus total halo mass. (3) The radial stellar mass and number density profiles
for the ensemble halo. We use a Ks-band selected catalogue for the 10 clusters
in the Gemini Cluster Astrophysics Spectroscopic Survey (GCLASS), with
photometric redshifts and stellar masses measured from 11-band SED fitting.
Combining the photometric catalogues with the deep spectroscopic component of
GCLASS, we correct the cluster galaxy sample for interlopers. We also perform a
dynamical analysis of the cluster galaxies to estimate the halo mass M200 for
each cluster based on a measurement of its velocity dispersion. (1) We find
that the central galaxy stellar mass fraction decreases with total halo mass,
and that this is in reasonable quantitative agreement with measurements from
abundance matching studies at z~1. (2) The total stellar mass fractions of
these systems decrease with halo mass, indicating that lower mass systems are
more efficient at transforming baryons into stars. We find the total stellar
mass to be a good proxy for total halo mass, with a small intrinsic scatter.
When we compare these results with literature measurements, we find that the
stellar mass fraction at fixed halo mass shows no significant evolution in the
range 0<z<1. (3) We measure a relatively high NFW concentration parameter c ~ 7
for the stellar mass distribution in these clusters. A simple model shows that
the stellar mass content of GCLASS can evolve in typical distributions observed
at lower redshifts if the clusters primarily accrete stellar mass onto the
outskirts. [Abridged]
