It does not change from release to release. Because GL does not include queries for the performance characteristics of an implementation, it is expected that some applications will be written to recognize known platforms and will modify their GL usage based on known performance characteristics of these platforms. They should be used by such platform recognition algorithms. Vendor specific information may follow the version number. Its format depends on the implementation, but a space always seperates the version number and the vendor specific information.
All strings are null-terminated.
If an error is generated, glGetString returns zero. The client and server may support different versions or extensions. The release number always describes the server.