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We present a detailed follow-up of the very energetic GRB 210905A at a highredshift of z = 6.312 and its luminous X-ray and optical afterglow. We obtaineda photometric and spectroscopic follow-up in the optical and near-infrared(NIR), covering both the prompt and afterglow emission from a few minutes up to20 Ms after burst. With an isotropic gamma-ray energy release of Eiso = 1.27E54erg, GRB 210905A lies in the top ~7% of gamma-ray bursts (GRBs) in terms ofenergy released. Its afterglow is among the most luminous ever observed. Itstarts with a shallow evolution that can be explained by energy injection, andit is followed by a steeper decay, while the spectral energy distribution is inagreement with slow cooling in a constant-density environment within thestandard fireball theory. A jet break at ~ 46.2+-16.3 d (~6.3 d rest-frame) hasbeen observed in the X-ray light curve; however, it is hidden in the H band dueto the contribution from the likely host galaxy, the fourth GRB host at z > 6known to date. We derived a half-opening angle of 8.4+-1.0 degrees, which isthe highest ever measured for a z>6 burst, but within the range covered bycloser events. The resulting collimation-corrected gamma-ray energy release of1E52 erg is also among the highest ever measured. The moderately largehalf-opening angle argues against recent claims of an inverse dependence of thehalf-opening angle on the redshift. The total jet energy is likely too large tobe sustained by a standard magnetar, and it suggests that the central engine ofthis burst was a newly formed black hole. Despite the outstanding energeticsand luminosity of both GRB 210905A and its afterglow, we demonstrate that theyare consistent with those of less distant bursts, indicating that the poweringmechanisms and progenitors do not evolve significantly with redshift.

A blast from the infant Universe: the very high-z GRB 210905A