They show it off with 4K monitors, just not their own. For a machine that's specifically slated to use them (6 thunderbolt ports, two GPUs) it's extremely strange behaviour.

Apple showed off Mac Pro with 4k screens, and advertised that the machine supports 3 4k monitors.

They have to ship their 4k monitors soon.

Are they "good enough"? I don't think there's a compelling reason to invest in one for my Late 2013 rMBP. And less to do so with the Mac Pro - I get a USB2 hub, no USB3. I have to use an adapter to use my Magsafe adapter. And if I have a Mac Pro, I get TB1, not 2.

It's not retina. 2560 x 1440 is the highest resolution.

It depends on what "Retina" means. It's resolution is close to the MacBook Pro, arguably it'll look just as good since it's further from your face. Or not.

http://store.apple.com/us/product/MC914LL/B/apple-thunderbol...

The 27" Thunderbolt Display (Cinema Display was discontinued in '11) has a smaller resolution than a 13" Retina Macbook Pro.

No, it’s not, not really, at any rate. (The way Apple defines it, a retina resolution is simply a resolution where individual pixels are not visible to someone with normal sight at a typical working distance. I think it’s a quite useful definition and I really want to use it outside the context of Apple products. I want to steal this trademark from Apple by turning it into a generic term. For example, at typical viewing distances 1080p TVs are retina screens. That means going to 4k for TVs isn’t really worth it unless you plan on getting a much bigger TV or sitting closer to your TV. But the following text will focus more on the technical aspects of actually making retina happen with OS X than this nifty definition of retina.)

Apple does quadrupling of the size of its UI (on their MacBooks and iOS devices) when switching from non-retina to retina.

Consequently even 4k is not really enough if they want to replace their 27" display. That 27" has a higher (physical and logical) resolution than 1080p and quadrupling turns a 4k display merely into (about) a 1080p display when it comes to its logical resolution.

You gain all that resolution but lose all that space. That’s in many ways an icky tradeoff. Yeah, Apple has a hacky way that increases the logical resolution, but it’s also an icky tradeoff. The UI is rendered at an higher resolution (quadrupled in size and all) than the display can show and then down sampled to display size – but that costs performance and also leads to slight blurriness.

Both are not very big issues (the Mac Pro should have enough performance to handle it and this is really more an issue on portable devices – but maybe you can cause issues by connecting multiple 4k displays; the resolution of those displays is so high that the slight blurriness is not very visible) but are also not optimal.

OS X simply is not dynamically scalable. It’s quadrupling or nothing. And that works very well, but it’s not as flexible as dynamic scaling.

Realistically Apple could go for a 4k 24" screen (where having merely about 1080p logical resolution would be acceptable) but I’m not sure if they want to.

But going even higher than 4k? To 5120×2880 (that would replicate the logical resolution of their current 27" at retina resolution)? I’m not sure whether that’s realistic or even possible on that machine.

As can be seen on the 13" retina MacBook Pro, Apple is willing to make icky tradeoffs in favour of less logical resolution (despite being their top of the line 13" it has a lower logical resolution than the non-retina 13" MacBook Air).

But it just seems that when it comes to the Mac Pro they currently don’t want to play ball at all. It will be interesting to see how they handle this.