NVIDIA has released a new beta graphics driver with OpenGL 4.4 support.
According to this message, here are the changes brought by R326.77:
This update fixes the following bugs reported in this forum thread: Comment #13: main() terminated prematurely Comment #22: More problems with samplers in structs Also fixed: Unable to allocate a DEPTH_COMPONENT16 sparse texture Rendering corruption with sparse depth textures Fix system instability when using multiple sparse textures
You can download NVIDIA OpenGL 4.4 drivers from THIS PAGE.
R326.77 exposes 317 OpenGL extensions like R326.29, the first OpenGL 4.4 driver.