Filler disfluencies--"uh" and "um"--are thought to serve distinct discourse functions. We examined fillers in spontaneous speech by youth with autism spectrum disorder (ASD), who struggle with pragmatic language, and by youth with ASD who have achieved an "optimal outcome" (OO), as well as in peers with typical development (TD). While "uh" rates did not differ, participants with ASD produced "um" less frequently than OO or TD groups. "Um" rate was associated with autism symptom severity, but not executive function or language abilities, suggesting that "um" serves a pragmatic, listener-oriented function. Moreover, in contrast to minimal production in ASD, the typical OO "um" production substantiates the normalization of subtle social communication in this population.