Abstract Background Hyperscanning captures interpersonal neural synchrony (INS) during social interaction. Objective To determine whether reduced INS characterizes autism spectrum disorder (ASD) or elevated autistic-like traits (ALTs). Methods A PRISMA search (updated April 25th, 2025) screened 1552 records; 20 studies met inclusion. Quality was appraised with modified CASP checklists. Results Sixteen interpersonal analyses across 20 studies (15 ASD, five trait-based) using varied neuroimaging modalities reported attenuated synchrony in 14 cases when an autistic or high-trait partner was present; effect direction varied with task design and dyad composition, indicating methodological contingencies rather than a uniform deficit. Heterogeneity precluded meta-analysis. Conclusions Reduced INS is a robust yet context-dependent correlate of autistic characteristics. Future work should directly test task- and dyad-level moderators.