The Kaveri APU launch driver is part of the fglrx 13.30 series and it's what I've been using in my AMD A10-7850K Kaveri Linux testing. It's not too much of a surprise seeing a new driver release for launch day as AMD has been kicking up with same-day support for Linux for several years now -- going back to the Radeon HD 4800 series -- with their Catalyst driver. If you're hoping for some major breakthroughs though with the new Catalyst Linux driver release, you will likely be disappointed.
In my testing of the driver over the past few days there were no major changes in OpenGL performance for existing Radeon hardware, there isn't any official Linux 3.13 kernel compatibility, and I didn't see any major bug-fixes. In fact, for some GPUs the fglrx 13.30.1 driver tested just led to problems with Unigine tests locking up for select GPUs. my earlier article. Stay tuned for the AMD Kaveri Linux benchmark results shortly; coming out today will be Windows 8.1 vs. Ubuntu Linux AMD APU numbers.