Language development in autism spectrum disorder (ASD) is heterogeneous, ranging from subtle differences to significant delays. In previous work, we identified three autistic language profiles in early childhood: Language Unimpaired (LU), Language Impaired (LI), and Minimally-Verbal (MV). While these profiles show distinct vocabulary, grammar, and pragmatic development, understanding their underlying neural correlates is essential to predict outcomes and develop targeted interventions. Here, we examined whole-brain resting-state EEG power across five canonical frequency bands in a longitudinal sample comprising 66 typically developing (TD) children and 122 autistic children (ages 1.6–6.0 years), yielding 358 time points. Within the ASD group, 61 children belonged to the LU profile, 44 children to LI, and 17 children to MV. Compared to TD peers, autistic children showed increased power in low-frequency (delta, theta) and high-frequency bands (beta, gamma). Gamma power varied by autistic language profile, with the highest levels in MV children. Moreover, gamma power within ASD followed a quadratic trajectory in relation to word combination acquisition, peaking around the time of acquisition and decreasing afterward. This pattern suggests a dynamic, compensatory mechanism supporting the transition to phrase speech, which is a critical milestone toward functional speech that may predict language outcomes in ASD.