As the Tony-winning revival of Chicago readies for its incredible 6,138th performance, the John Kander and Fred Ebb musical has two special milestones to celebrate. Not only will it become the fourth-longest running show in Broadway history (surpassing the original mounting of A Chorus Line), but the show will also have the distinction of becoming Broadway's longest running American musical (British imports The Phantom of the Opera, Cats and Les Miserables currently lead the pack of long-running tuners.) On August 26, show stars Nikka Graff Lanzarone, Charlotte d'Amboise and Christopher Sieber gathered backstage at the Ambassador Theatre with special guest Bebe Neuwirth (who scored a Tony for playing Velma Kelly when the revival began its run in 1996) to celebrate the milestone. Take a look at the historic evening below!