<p>The economic potential of AI systems lies in augmenting human labour, creating hybrid intelligence where humans and AI complement each other. Central to this relationship is the integration of human mental effort, involving cognitive engagement and decision-making, contributing to interaction between humans and AI. If AI systems supplement instead of substitute individuals, the inquiry arises about how AI affect the quality of human work, particularly in terms of mental effort and engagement. A suitable concept to capture this impact is meaningful work, perceived as valuable and significant to individual’s ideals or standards. Meaningfulness of work is critical in hybrid intelligence systems, addressing qualitative dimensions of human labour that AI cannot easily replicate. This paper presents an experimental study examining how AI system use affects perceived work meaningfulness, with mental effort as a key mediating variable. We conducted an experimental study with a writing task, for which we randomly assigned respondents to a group that used or did not use an AI-based text generator. After completing the task, 677 respondents evaluated the meaningfulness of the task and their contribution to the assignment. The findings reveal that while the deployment of AI systems showed no direct effect on task meaningfulness, mental effort emerges as a critical mediating variable in the relationship between AI support and perceived meaningfulness. This mediation effect represents the study’s primary contribution, demonstrating that the impact of AI on work meaningfulness operates indirectly through changes in cognitive engagement rather than through direct effects.</p>