Sony Pictures Classics has paid north of $3.5 million for Mike Mills’ “Thumbsucker,” taking North America and select international territories.The dark coming-of-age comedy concerns a high schooler whose life spins into turmoil when he tries to break his thumbsucking habit. Mills adapted the script from Walter Kirn’s novel. Pic’s star, Lou Pucci, won a special jury prize at the Sundance Film Festival for his performance. UTA repped the filmmakers in the deal. Cast includes Tilda Swinton and Vincent D’Onofrio, with Keanu Reeves, Vince Vaughn and Benjamin Bratt in supporting roles. “Thumbsucker” next plays at the Berlin Film Festival, where it will vie for the Golden Bear in the main competition.