["Autism Research, EarlyView. ", "\nABSTRACT\nThe P100/P100m component of auditory event‐related potentials/fields is considered a potential biomarker of atypical arousal and language difficulties in children with ASD. When elicited by complex speech‐like sounds with regular temporal or frequency structure, P100/P100m may be influenced by sustained negativity (SN), which can reduce its amplitude due to opposing current polarity and contribute to ASD‐related differences. Using magnetoencephalography (MEG), we examined P100m responses to acoustic regularities in the left and right auditory cortices in 35 ASD and 39 TD boys (7–12 years). Stimuli included (1) temporally and spectrally regular sounds (periodic vowels), (2) temporally regular sounds (periodic non‐vowels), (3) spectrally regular sounds (non‐periodic vowels), as well as (4) non‐regular control stimuli (non‐periodic, non‐vowels). P100m was estimated using distributed source localization. Both groups showed decreased P100m amplitude and latency with acoustic regularities, accompanied by proportional SN increases, suggesting P100m modulation primarily reflects early SN enhancement. No group differences were observed in P100m latency or amplitude, and their modulation by stimulus type was also normal in ASD, indicating spared processing of acoustic regularities in the P100m time range. However, P100m latencies variability was increased in boys with ASD, and their left P100m amplitudes to both non‐regular and regular sounds were negatively associated with cumulative language and intellectual abilities. These findings suggest that while most children with ASD show typical P100m responses, individual variations in P100m amplitude may reflect neurodevelopmental differences in cortical maturation and/or sensory habituation processes that contribute to the heterogeneity of cognitive and language abilities in ASD.\n"]