Mids says mag3, but I have no way to personally verify that as I haven't taken a corrupter up very high just yet.
I can't verify anything but I'm pretty sure Castle made all version of Total Focus mag 3.
Thanks for the help all. 
Defenders and Corruptors use the exact same Power Mastery pool. The fully-qualified name of the power is Epic.Power_Mastery.Total_Focus for both ATs.
http://www.fimfiction.net/story/36641/My-Little-Exalt
What is the mag stun of Total focus from the corruptor epic power mastery pool? Is it mag 3 just like the Defender epic power mastery pool, or has it been changed to mag 4? I looked on the Red Tomax site and searched the forums with nothing coming up conclusively.
Thanks in advance.