Artificial intelligence (AI) technologies, particularly AI-generated summaries (AIGS), are reshaping user interactions and decision-making processes on digital content consumption platforms by altering the way information is presented and processed. Grounded in the Cognitive Miser Theory, this study conducted a field experiment on a leading Chinese video social media platform to examine the impact of AIGS on user endorsement behaviors (e.g., likes, coin-tipping, and favorites) and commenting behaviors. The results show that AIGS reduces users’ cognitive load in watching and comprehending videos, thereby positively influencing both endorsement and commenting engagement. Further analysis reveals that AIGS significantly alters the hierarchical structure of video comments by reducing parent comments and increasing child comments. From a cognitive perspective, this study reveals the double-edged sword effects of AIGS as an information-processing tool, contributing to the theoretical understanding of AI applications and platform governance.