In an event that appears to be very much like the amazing multi-part 25th anniversary/2009 season finale TMNT Forever in which the Turtles from various dimensions and iterations crossover to battle Krangs. They are even keeping with the altered art styles (the old 2D animation and the more modern 3D animation) for each of the Turtles as they travel between times. It's reported that TMNT creator Kevin Eastman's Mirage Studios Teenage Mutant Ninja Turtles comic book series will be appearing as well- just like in TMNT Forever.
The 1980's Turtles themselves will be voiced by the original cast, as well as Krang's original voice actor Pat Fraley.
For more of my Turtles related posts [ TMNT ]
Source [ IGN ]