This paper centers on how L2 learners bid a first idea in opening of task-based text-chat interactions. How first ideas are bidded is sensitive to learners' level of L2 interactional ability. Lower-level learners are more likely to reply an idea proffer with another idea proffer. High-level learners tend to make more expanded sequences around first idea proffers and search for ideas. CA can be profitably fit to text-chat interaction to track evolution of L2 interactional ability.