First beta of OS X Mavericks 10.9.3 which was released yesterday came with no change-log. There was no mention about new features or any major bug fix. Apple just mentions that developer should test the build for audio and graphics.
But apart from all these there is one new feature present in the beta which is not mentioned by apple. The first beta of OS X 10.9.3 adds a native ‘Retina” resolution option for 4K displays. It enables all compatible 4K displays to be set at a “Retina” resolution, there is also an option for 60Hz output. Macrumors reported about the new feature. It was tested on both Retina MacBook Pro and latest Mac Pro with Dell Ultrasharp 24 HD Monitor and it works perfectly.
MacRumors further says that:
To this point, OS X compatibility with 4K displays has been known to be somewhat erratic, as AnandTech revealed in December that Sharp’s 32” 4K display supported only one scaled resolution at 2560 x 1440. Furthermore, it was discovered that Apple had chosen to render text, menu and UI elements in the same manner as the Retina MacBook Pro, resulting in small and difficult to read on-screen elements on a 4K display. Various other 4K monitors were also found to be not properly supported.
Native Support for 4k displays indicates that Apple is preparing for hogher resolution ThunderBolt Display, as it was introduced two years ago and is in the pipeline to be refreshed. It is long rumored that Apple will launch 4K display now this support confirms the reposts.