["Autism Research, Volume 19, Issue 4, April 2026. ", "\nABSTRACT\nIdentifying early markers for autism spectrum disorder (ASD) is a clinical priority. This study investigated interpersonal affect synchrony (IAS) as a measure of interactional quality in a longitudinal cohort of 90 high‐risk infants. We aimed to disentangle its contribution from mutual gaze and identify data‐driven social interaction profiles linked to sensory traits. Parent‐infant interactions were recorded at 6–18 months; IAS was quantified using Cross‐Recurrence Quantification Analysis, and ASD outcomes were determined at 18–24 months. Infants later diagnosed with ASD (n = 25) showed significantly lower IAS (F(1,84) = 5.89, p FDR = 0.023) and synchrony stability (F(1,84) = 5.37, p FDR = 0.023) than non‐diagnosed infants (n = 65), yet the groups did not differ in mutual gaze (p = 0.200). Logistic regression analysis further showed that IAS (OR = 0.561, p FDR = 0.038) and synchrony stability (OR = 0.013, p FDR = 0.038) both significantly predict clinical outcome. K‐means clustering revealed three profiles: “High Gaze‐High Synchrony,” “Mid Gaze‐Low Synchrony,” and “Low Gaze‐High Synchrony.” The “Mid Gaze‐Low Synchrony” profile was significantly associated with a later ASD diagnosis (p adj = 0.031), while the “Low Gaze‐High Synchrony” profile was linked to higher sensation‐seeking traits (p adj = 0.028). The quality of parent‐infant affective connection is a more robust early marker for ASD than the quantity of mutual gaze. These findings reveal critical heterogeneity, identifying a high‐risk “gaze without engagement” pattern and a potential adaptive pathway to synchrony, underscoring the need for individualized strategies in early screening and intervention.\n"]