The alcohol treatment literature has established in-session client speech as a mechanism of change that therapist behavior can influence and that can predict drinking outcomes. This study aimed to explore temporal patterns of in-session speech in Alcohol Behavioral Couple Therapy (ABCT), including the unique interplay between client and partner speech and the role of speech trajectories in predicting client drinking outcomes. Participants were 165 heterosexual couples receiving ABCT in one of four clinical trials. We coded client speech on an utterance-by-utterance basis using the System for Coding Couples' Interactions in Therapy–Alcohol. We focused on individual-level speech codes of change talk and sustain talk and couple-level variables of positive and negative interactions. We segmented the initial and midtreatment sessions into quartiles to conduct path analyses and latent growth curve models. Path analyses suggested that clients and partners may not have been aligned in terms of treatment goals at the start of the therapy. This misalignment within couples was pronounced during the initial session and decreased by the midtreatment session, reflecting progression toward treatment goals. Of the latent growth curve models, only client sustain talk during the midtreatment session predicted greater client drinking at the end of treatment. Results provide insight into the inner workings of ABCT and suggest recommendations for ABCT therapists. This study also supports a growing consensus that sustain talk may be a stronger mechanism of change than change talk in various alcohol treatment interventions. •In Session 1, client CT11CT = change talk predicted partner ST,22ST = sustain talk which then elicited client CT.•By mid-treatment, partner CT predicted higher client CT and lower client ST.•Couples' language became more aligned over the course of treatment.•Higher client ST during mid-treatment predicted higher follow-up drinking.