No all 360 discs are Dual Layer so they fit ~9.2GB but the new disc that they are using can hold I believe close to ~10 or 11GB.
They're still single-side DVD-9 discs, so the maximum theoretical size is 7.95GB; the 360 discs also have some sort of copy protection/update sector so a bit of that space is automatically compromised. The maximum size of actual game data on the previous discs was 6.8GB; even with the newer type I've never seen one larger than 7.7GB.
EDIT: The largest single disc-size currently appears to be Dragon's Dogma, which is 7.9GB.
Edited by Derfel, 17 September 2012 - 11:14 AM.