Although conversation openings and closings are ritualized speech acts (House & Kádár, 2023), they do require interactional work (Schegloff, 1986). Thus, they are important elements of interactional competence (Roever, 2022) and have been studied extensively in L2 interactions, including various types of technology-mediated communication contexts (e.g., Abe & Roever, 2019; 2020). However, to our knowledge, no research on openings and closings has been conducted with newer technologies such as spoken dialogue systems (SDS). To address this gap, this study compares conversation openings and closings across two modalities: a role-play with a human interlocutor versus with a fully automated agent. We analyzed interactional data from 47 tertiary-level learners of English. A quantitative (e.g., number of turns) and a qualitative, discursive analysis rendered several key findings: 1) learners were more transactionally oriented in SDS modality, but tended to engage in relational discourse with a human interlocutor; 2) humans adapted to the emergent discourse in both modalities; 3) despite training, the human interlocutor was inconsistent in displaying transactional versus interactional patterns with different participants, while the SDS followed the same dialogue structure in each interaction. Findings will be discussed in terms of specific affordances of the two modalities for interactional competence.