["TESOL Quarterly, EarlyView. ", "\nAbstract\nWhile generative artificial intelligence tools have been increasingly integrated into language education to optimize learners' learning outcomes, the effects of ChatGPT on EFL learners' oral presentation performance, critical thinking, enjoyment, and motivation have not been fully explored. Although traditional AI chatbots have shown potential in language learning support, their reliance on fixed interaction paths and limited capacity for human‐like dialogue have constrained their effectiveness in cognitively demanding tasks such as oral presentation preparation. To address this gap, this study drew on Activity Theory (AT) as a theoretical lens to examine how generative AI (GenAI) mediates EFL oral presentation preparation in flipped classrooms. A quasi‐experiment was conducted to evaluate the effects of GenAI intervention. Two intact classes with 99 EFL students (without GenAI experiences) were randomly assigned to either an experimental (n = 49) or control (n = 50) group. The experimental group (EG) used both search engines and ChatGPT, while the control group (CG) only used search engines. The results demonstrated that students in EG exhibited significantly higher levels of critical thinking disposition (CTD) and enjoyment compared to those in CG. Notably, there were no significant differences in learning motivation between the two groups. Furthermore, students in EG received higher oral presentation scores. During the interviews, participants highlighted that ChatGPT helped offload cognitive demands related to information processing, allowing them to allocate more mental resources toward thinking more comprehensively and critically about the presentation topic. This study is among the first to propose and validate the use of GenAI to free cognitive capacity to address critical thinking challenges in the context of EFL oral presentations, while also enhancing learning enjoyment within a flipped classroom setting.\n"]