It's actually more of a 3-3-5. And yeah, they finally decided to make some adjustments and get more speed on the field to defend against all the spread offenses.
The biggest difference is they are actually playing LBs this year. Last year they practically phased the LBs completely out of the game. That's why guys like Tom Wort who had no business jumping to the NFL decided to leave early. He and the other LBs weren't getting any playing time.
The result was Oklahoma being unable to stop the run.
Stoops and his brother admitted they made a huge mistake, even going so far as to apologize to the LBs, and the result is the LBs are playing more and the run defense has been a hell of a lot better than it's been in recent years.