pyglet provides an interface to OpenGL and GLU. The interface is used by all of pyglet's higher-level API's, so that all rendering is done efficiently by the graphics card, rather than the operating system. You can access this interface directly; using it is much like using OpenGL from C.
The interface is a "thin-wrapper" around libGL.so on Linux, opengl32.dll on Windows and OpenGL.framework on OS X. The pyglet maintainers regenerate the interface from the latest specifications, so it is always up-to-date with the latest version and almost all extensions.
The interface is provided by the pyglet.gl package. To use it you will need a good knowledge of OpenGL, C and ctypes. You may prefer to use OpenGL without using ctypes, in which case you should investigate PyOpenGL. PyOpenGL provides similar functionality with a more "Pythonic" interface, and will work with pyglet without any modification.