The integration of generative artificial intelligence (AI) into higher education has presented universities with an unprecedented situation. In the context of written production, this change affects the very nature of the teaching situation. This article aims to examine the impact of the spontaneous use of AI tools on language skills, autonomy and cognitive effort. To this end, learning practices must be rethought. Using a mixed-methods approach, our research combines a questionnaire distributed to 92 students, a comparative writing task (with and without AI), and direct observation of practices carried out with a subsample (n=5). Through a cross-analysis of these declarative, behavioural and performance data, this study aims to examine the actual benefits of technological mediation. The objective of this research is to determine whether these new tools constitute a genuine lever for learning that promotes autonomy, or whether, on the contrary, they lead to a passive delegation of intellectual effort and a dependence on software in language classrooms.