What is currently being thought of as the "pilot" of Addison Shephard's supposed spin-off, an episode that will air later this season (but is thought to be episode 319), My Favorite Mistake, will be a two-hour episode! Awesome! Here's the full press release from ABC:

Acclaimed actor Taye Diggs will guest star in "Grey's Anatomy" in a special two-hour episode that will air later this season. "Grey's Anatomy" also welcomes Emmy-winning actor Hector Elizondo, who is currently in production as Mr. Torres, Callie's father. The "Grey's" episode, entitled "My Favorite Mistake," has not yet been assigned an airdate.