Background <p>Sudden gains (SGs) are large, stable symptom reductions that occur between consecutive therapy sessions and are associated with superior treatment outcomes. To better understand the processes that give rise to SGs, the present study examined session-to-session changes in maintaining variables among individuals with social anxiety disorder (SAD).</p> Methods <p>Participants were 105 adults (aged 19 years and older) diagnosed with SAD and receiving cognitive behavioral group therapy. Multilevel modeling was used to compare treatment outcomes between individuals with and without SGs. We also analyzed changes in social probability bias, social cost bias, self-focused attention, fear of negative evaluation, safety behaviors, and negative social self-beliefs surrounding SGs.</p> Results <p>Of the total sample, 39 participants (37.1%) experienced at least one SG and demonstrated greater reductions in social anxiety symptoms at posttreatment and follow-up than those without SGs. In the session preceding an SG, social cost bias, safety behaviors, and negative social self-beliefs decreased. During the SG session, all cognitive, behavioral, and symptomatic indicators of SAD showed significant decreases. Following the SG session, reductions in social cost bias and negative social self-beliefs continued.</p> Conclusions <p>This study identified distinct patterns of change in maintaining variables surrounding SGs in SAD, offering insights into the processes of change that may contribute to improved treatment outcomes.</p>