It's already been renewed. I came across this on imdb:
The CW on Monday announced early pick-ups for three of its series: Supernatural, The Vampire Diaries and Arrow.
Arrow gave The CW its best series premiere since 2009, Vampire Diaries is the network’s highest-rated show in target demos and Supernatural is up 15 percent in total audience versus last season. The dramas will be entering their second, fifth and ninth seasons in fall 2013, respectively.
“We said last year that one of our goals was to establish building blocks to grow on, and now with our new hit »
- Matt Webb Mitovich