Like last season (and the season before that), Grey's Anatomy has been renewed for 23 more episodes for it's fourth season. Obviously, ABC can up that order (as evidenced by the fact that season two had 27 episodes, and season three had 25) if they want to (and hopefully they'll want to), but at the moment, 23 is the number they've decided on. The first of 23 all-new Grey's airs on Thursday, September 27.