My current mac pro has 6 displays attached, three of which are "high resolution" (2560x1600).

I think that the 4k displays require 2x thunderbolt ? Or else why would there be a limitation of 3 ?

So all 6 TB ports used, and no ability to add a 4th display.

EDIT: well, I could add a 4th with HDMI, but it would be low resolution, and the 5th and 6th displays are impossible. Also, all 6 TB ports used up, so no further expansion is possible.

I believe Thunderbolt 2 only needs one port for 4k. (http://mashable.com/2013/06/05/intel-thunderbolt-2/)

Thunderbolt can be daisy-chained just like USB, so you're not limited to just the 6 provided ports.

"Thunderbolt can be daisy-chained just like USB, so you're not limited to just the 6 provided ports."

Ok. Still trying to understand the "3" limitation on 4k displays. If it's a bandwidth issue, you'd think the number would be 4, since there are two cards.

And if it is bandwidth, then presumably 3 4k displays plugged in and ... even the empty TB ports become unusable since there is no more bandwidth available ?

I just want to plug in 6 monitors and am trying to figure out how :)

It's bandwidth of the HDMI interface (is my understanding), but even then, the max of a standalone AMD or nVidia graphics card is typically three displays. And these are 4K displays!

It certainly could be a bandwidth issue. Assuming 4K=3840x2160, that's about 12 Gbits per display with 24 bits/pixel and 60 Hz.

Wait till the actual release date! There is not a good reason for them to announce new apple displays until they can actually be used with their hardware. Thunderbolt 2 doesn't even exist yet.

He mentioned "...your favorite 3rd party displays" when introducing the 4K-ness.