Traditional firms that used to rely on high quality, internal R&D, and slow development cycles are facing major demands in the increasingly dynamic and open markets. They are facing both strategic transformation from closed to open innovation, which brings along cultural and behavioral challenges. This study examines an in-depth case study of European B2C firm, which unravels the open innovation transition journey focusing on two key dimensions - ecosystem strategy and ambidextrous organizing. We find that the case company has undergone the transition in three particular phases, with implications to the organizational boundaries (ecosystem strategy) as well as how they deal with contradictory exploitation and exploration tensions (ambidextrous organizing).