The 2013Q4 highlights are: OpenGL 3.3 API support, Fast Boot support and, power savings features.
OpenGL 3.3 API supported landed in Mesa 10 along with new GL extensions.
Fast Boot support on 2D side had already being released on previous 2013Q3, but now it is fully functional with Kernel support. It might be need require to enable it on your BIOS configuration.
The power features PC8+ and eDP Panel Self Refresh (PSR) landed on this kernel for 4th Generation Intel® Core™ processors with Intel HD Graphics.
Components of this stack are:
For more details read the full release notes: https://01.org/linuxgraphics/downloads/2013/2013q4-intel-graphics-stack-release