GRB with redshift 6.3 has been detected recently, which indicates that GRBs now begin to serve as probes of the high-redshift cosmology.

It's sort of pioneering in many ways, because doing this kind of detailed study of a galaxy at a very high redshift is extremely difficult.

Such a high redshift indicates the galaxy is 9.3 billion light years away, so we see it just 4.4 billion years after the Big Bang.