NVIDIA Already Publishes An OpenGL 4.5 Linux Driver
While the OpenGL 4.5 specification is fresh off the press and we haven't even seen the Khronos SIGGRAPH announcement yet, NVIDIA has already made public their OpenGL 4.5 beta drivers for Linux and Windows.
The NVIDIA 340.23.01 Linux driver is available today and provides beta support for OpenGL 4.5 and the OpenGL Shading Language (GLSL) 4.50 versions. For tapping all of the potential of OpenGL 4.5, a Fermi, Kepler, or Maxwell GPU is needed. This is conveniently the GeForce 400 series and newer, which is only what's supported now after NVIDIA dropped pre-Fermi support from their mainline Linux driver.