Gran Turismo 6 Already Being Worked On
DLC for Gran Turismo 5 is still coming, but Polyphony is working on their next game as well.
Kazunori Yamauchi
Gran Turismo 6 In Development
GT5 is done, and Kazunori Yamauchi indicates that GT6 is already underway.
Gran Turismo Creator Yamauchi Presenting at D.I.C.E. Summit
Polyphony Digital's Kazunori Yamauchi, industry veteran Mark Cerny and others comprise the initial speaker lineup for the 2011 D.I.C.E. event.
Gran Turismo 5 Cost $60 Million to Make
And Polyphony Digital's Kazunori Yamauchi considers that to be a "fairly small amount."