King Kostya unfortunately is too old, and I think he is happily retired in Australia. I am still wishing he would fight one last time.
He recently retired but i think it has been safe to say that he has been retired since the Hatton defeat and he was probably semi retired before the Hatton fight. Having said that he was one of the greatest boxers of the modern age and the first and only man to unify the titles at 140. Plus he was/is a great ambassador to the sport of boxing itself.
Kostya was never very active even when he was fighting. He would only fight once or twice a year - if that, and would take long breaks. Kostya Tszyu gets treated like he's Jesus Christ in Australia. He stopped fighting for the fans a very long time ago. The money and the fame became more important to Kostya. He changed after he blew up, and then he turned his back on the sport.
Retired out of shame, losing to a darts player...just as we were getting over the Vince Phillips debacle :-( I loved watching him in his prime.