Employing a CA-inspired methodological approach, this study investigates L2 learners' interactional competence for dyadic interaction via text chat. Fifty-three dyads of Japanese learners of English at three proficiency levels (high, mid, and low) participated in this study, where they worked on three discussion tasks in L2 English. The data were 97 participant-generated task closings, which were analyzed in terms of linguistic repertoire and sequence organizations of terminal exchanges between participants in a dyad, and summons-answer sequences between participants and the researcher. The data showed that the participants recurrently implemented a sequence of soliciting and providing an agreement on the idea for task accomplishment to signal a forthcoming closing of task talk. The findings indicated that more proficient learners produced more extended sequences in conducting closing rituals. Some high-proficiency learners explicitly mentioned, or interacted with, the researcher, a third party, to initiate task closing or reformulate crossed messages in closing the talk. These findings provide insights into online L2 interactional competence in text-based CMC media.