Artificial Intelligence (AI) adoption and benefits are not well understood yet in businesses, leading to a low rate of adoption success by companies. The well-known Unified Theory of Acceptance and Use of Technology (UTAUT) and its extensions do not account for AI and specific business size specificities. In this context, this study’s primary goal is to propose a new model inspired by UTAUT to account for AI-based IS and distinct business sizes’ specificities. The proposed Artificial Intelligence Adoption Intention Model (AI2M) was tested using a sample of 363 participants, confirming the significance of UTAUT’s influencing factors: Perceived Performance, Social Influence, and Expected Effort. Furthermore, distinctly to the context, UTAUT was proposed, Facilitating Condition was found to influence Behavior Intention. In addition, mediation tests revealed that Self-efficacy and Social Influence mediate the effect of the other three factors on the adoption intention. Finally, a moderation relationship was found between the company’s size on the effect of self-efficacy and social influence on the adoption intention. AI2M explains 48% of the variance of the adoption intention, reaching generalization for different business sizes. Therefore, the present study helps reduce the gap in studies related to technology adoption and the adoption of AI-based technologies in companies of distinct sizes, supporting future academics’ investigations and managers’ decisions.