If it follows the established pattern, then it might be level 65, but Wowwiki is suggesting it will be level 70.
Current benchmark levels are:
Level 20 for 151-225
Level 35 for 226-300
Level 50 for 301-375
So, it might make sense if the 15-level increment was utilized making it were level 65 to train for 376-450.
But, it might also be lower...I found
this site with a screenshot of the enchanting trainer (scroll down) that says Level 60 and Enchanting level 350 is required to train Grand Master (450).
It's still beta though, so things can change.