  We use deep follow-up XMM-Newton observations of 6 clusters discovered in the
XXL Survey at $z>1$ to gain robust measurements of their X-ray properties and
to investigate the extent to which scaling relations at low redshift are valid
at $z>1$. This sample is unique as it has been investigated for AGN
contamination, which ensures measurements are not undermined by systematic
uncertainties, and pushes to lower mass at higher redshift than is usually
possible, for example with Sunyaev-Zel'dovich (SZ) selected clusters. We
determine the flux contribution of point sources to the XXL cluster flux in
order to test for the presence of AGN in other high-redshift cluster
candidates, and find 3XLSS J231626.8-533822 to be a point source misclassified
as a cluster and 3XLSS J232737.3-541618 to be a genuine cluster. We present the
first attempt to measure the hydrostatic masses in a bright subsample of $z>1$
X-ray selected galaxy clusters with a known selection function. Periods of high
particle background significantly reduced the effective exposure times of
observations (losing >50% in some cases) limiting the power of this study. When
combined with complementary SZ selected cluster samples at higher masses, the
data appear broadly consistent with the self-similar evolution of the low
redshift scaling relations between ICM properties and cluster mass, suggesting
that properties such as the X-ray temperature, gas mass and SZ signal remain
reliable mass proxies even at high redshift.
