Board Thread:Questions and Answers/@comment-10797017-20130622101437/@comment-11051098-20140606010240

He found out that his old Zanpakutô was fake, since it had no Asauchi. Zangetsu was forged with an Asauchi and Ichigo now has a complete Zanpakutô. As far as I can tell, it's still in a constantly released Shikai form, and I do believe the dual blade is his Shikai.

Remember that it was revealed that he only used a fraction of his full power before. All things considered, I think his "new" Bankai should be even more powerful than the level he has demonstrated by now.