The system with c6-d5 in the Grunfeld Fianchetto has been played in thousands of games, even at the world championship level. It's one of Black's most solid options.
1. g1f3  1... d7d5  2. g2g3  2... g7g6  3. d2d4  3... f8g7  4. c2c4  4... c7c6  5. f1g2  5... g8f6  6. e1g1 