apparently 54,000. Seems like it is including even fictional words though in this test (like from fiction novels). Ironically I scored higher on the expert words (18/20) than the "advanced" words (11/20)
quixotic, scrooge, shangri-la, Uncle Tom, gargantuan, kafkaesque, blurb, milquetoast
and words like cyberspace were first used in fiction
once real people use them, they stop being fictional words