Showrunner Shonda Rhimes posted the below message on her production company's website this morning:
October 19, 2012 - I'm sad to say that Private Practice's run will end after episode 613 this season. There was a lot of discussion and debate but, in the end, the guys at the network and the studio and I all decided that Private Practice was reaching its finish line. Creatively, we are all extremely proud of the show and especially proud of this season -- which you will all soon discover is a creative renaissance. I can't wait for you to see it.
It's heartbreaking to end. Truly. I feel so lucky to write for these characters and tell these stories and I truly feel this show has taught me so much as a writer. And there's a family here, of crew and cast, people who have bonded over these past five and a half seasons. It's rare for a show to go for more than 100 episodes and we are incredibly proud to have been such a show. And we're grateful to all of you for spending time with us for an hour every week for the last 6 years. It's meant the world.
This shouldn't be a big surprise, especially to fans of the series, who will remember that star, Kate Walsh, announced that she would be leaving back in May.
Of course, Audra McDonald left Private Practice at the end of season four.
Taye Diggs on the other hand has been part of the starring cast since the first season, and still is.