  We present results from a 100 ks XMM-Newton observation of galaxy cluster
XLSSC 122, the first massive cluster discovered through its X-ray emission at
$z\approx2$. The data provide the first precise constraints on the bulk
thermodynamic properties of such a distant cluster, as well as an X-ray
spectroscopic confirmation of its redshift. We measure an average temperature
of $kT=5.0\pm0.7$ keV; a metallicity with respect to solar of
$Z/Z_{\odot}=0.33^{+0.19}_{-0.17}$, consistent with lower-redshift clusters;
and a redshift of $z=1.99^{+0.07}_{-0.06}$, consistent with the earlier photo-z
estimate. The measured gas density profile leads to a mass estimate at
$r_{500}$ of $M_{500}=(6.3\pm1.5)\times10^{13}M_{\odot}$. From CARMA 30 GHz
data, we measure the spherically integrated Compton parameter within $r_{500}$
to be $Y_{500}=(3.6\pm0.4)\times10^{-12}$. We compare the measured properties
of XLSSC 122 to lower-redshift cluster samples, and find good agreement when
assuming the simplest (self-similar) form for the evolution of cluster scaling
relations. While a single cluster provides limited information, this result
suggests that the evolution of the intracluster medium in the most massive,
well developed clusters is remarkably simple, even out to the highest redshifts
where they have been found. At the same time, our data reaffirm the previously
reported spatial offset between the centers of the X-ray and SZ signals for
XLSSC 122, suggesting a disturbed configuration. Higher spatial resolution data
could thus provide greater insights into the internal dynamics of this system.
