Apple annonunced that all new Mac models as of January 2003 will only boot into Mac OS X. Classic compatibility will remain.
Now its time for Apple and our third-party developers to focus all of our resources exclusively on Mac OS X, rather than dividing them between two different operating systems. -- Steve Jobs.
Apple's removal of OS 9 support has been rumored as far back as June 2002 with further hints in August (1, 2)