  High redshift AGN holds the key to understand the early structure formation
and to probe the Universe during its infancy. We review the latest searches for
high-z AGN in the deepest X-ray field so far, the Chandra Deep Field South
(CDFS) 4 Msecond exposure. We do not confirm the positive detection of a signal
in the stacked Chandra images at the position of z~6 galaxies recently reported
by Treister and collaborators. We present z>3 X-ray sources number counts in
the 0.5-2 keV band obtained joining CDFS faint detections with Chandra-COSMOS
and XMM-COSMOS detections. We use these number counts to make predictions for
surveys with three mission concepts: Athena, WFXT and a Super-Chandra.
