QSO J0313−1806 was the most distant, and hence also the oldest known quasar at z = 7.64, at the time of its discovery. In January 2021, it was identified as the most redshifted (highest z) known quasar, with the oldest known supermassive black hole (SMBH) at (1.6±0.4)×10 solar masses. The 2021 announcement paper described it as "the most massive SMBH at z > 7". This quasar beat the prior recordsetting quasar, ULAS J1342+0928. In 2023, UHZ1 was discovered, setting a new record for most distant quasar, eclipsing that of QSO J0313−1806.
One of the 2021 paper authors, Feige Wang, said that the existence of a supermassive black hole so early in the existence of the Universe posed problems for the current theories of formation since "black holes created by the very first massive stars could not have grown this large in only a few hundred million years". The redshift z = 7.642 corresponds to an age of about 600 million years.
