CL J1001+0220 is, as of 2016, the most distant known galaxy cluster. Discovered in 2016 by the Chandra X-ray Observatory in conjunction with the ESO's UltraVISTA telescope and the Atacama Large Millimeter Array, it has a redshift of z=2.506, placing it at a distance of 11.1 billion light-years from Earth. The galaxy cluster appears to be undergoing the transformation from a galaxy cluster that is still forming, a proto-cluster, to a mature cluster, and it is the first such cluster observed in this stage of its evolution.