Latest OS X 10.9.3 Beta allows external 4K monitors to run at Retina resolution

Earlier today, Apple provided developers with the first beta for the upcoming release of OS X Mavericks version 10.9.3. Apple did not disclose any new features coming in 10.9.3, but we have discovered that the update includes notable enhancements for users with Macs connected to 4K-resolution monitors. With 10.9.3, Mac users can now natively set their 4K monitors to run the Mac operating system at a pixel-doubled “Retina” resolution.

Mark Gurman | 9to5Mac

Don't think we're too far from 4K Cinema Display and more relevant for me, a 27" Retina iMac.