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The cluster of galaxies Abell~2163 is exceptional in its X-ray luminosity ($L_{X\,(0.5-4.5\rm\,keV)} \sim 1.2 \times 10^{45} \, h^{-2} \rm \, erg \, s^{-1}$), which arises from the hottest known X-ray atmosphere ($kT \sim 14 \rm\, keV$; Arnaud et al. , ApJ, 390 , 345). Our observations of the cluster with the VLA show that it is also exceptional in the radio band: it hosts a halo of size $\sim 1.2 h^{-1} \rm\,Mpc$, which makes it the largest such source. Its bolometric luminosity of $1.2\times 10^{42} \, h^{-2} \rm\,erg\,s^{-1}$ (from 10\,MHz to 10\,GHz, emitted) is an order of magnitude larger than that of the most luminous radio halo reported previously. As much as 10\% of the cluster's X-ray luminosity in the $0.5-4.5\rm\,keV$ band may be produced by the inverse-Compton scattering of cosmic microwave background photons by the halo's relativistic electrons.
