A single crystal of fully dehydrated sodium zeolite X, Na92Al92Si100O384 per unit cell, reacted with cesium vapor at 450 degrees C. Its structure was determined by X-ray diffraction methods at 24 degrees C in the cubic space group Fd $$($) over bar 3 (a = 25.155(3) Angstrom). Not only have all 92 Na+ ions been replaced with Cs+ by redox reaction, but an additional 36 atoms of Cs were sorbed to give Cs128Al92Si100O384. Most cesiums participate in a cationic continuum with a formula of (Cs-122)(86+) per unit cell. An additional six Cs+ ions are found at the centers of double six-oxygen rings. The continuum, per unit cell, consists of eight prismatic clusters, six of which are icosahedral (12 cesiums) and two of which are expanded to contain an additional cesium atom. Each cluster contains a cesium atom at its center (at the center of zeolite X’s supercage). These clusters, arranged as the carbon atoms in diamond, are tetrahedrally connected to give the continuum, filling all supercages. Each sodalite cavity contains two cesiums (at sites I’ and II’) which attach to the continuum, one per cluster, via a large-cavity cesium at site II, I’, II’, and II are linear with intercesium distances of 3.89(2) and 3.92(2) Angstrom. Each cluster plus I’-II’ appendage contains 4.5 electrons on average, one of which should reside principally on the cesium at the cluster center and another principally in the sodalite unit. The remaining electrons appear to be widely delocalized as in a metal.