This study examines the influence of ChatGPT on tourist behaviour using complexity theory. Factors such as media richness, anthropomorphism, trust in ChatGPT, and trust in online travel agencies are investigated to understand their effects on purchasing intentions and word-of-mouth, along with a moderator of sustainable-tourism action (practice). Results revealed the relationships among the variables, highlighting the crucial role of trust in shaping consumer behaviour. A comparison between high and low levels of sustainable-tourism practice groups provides further insights. The study discusses implications for the travel industry, emphasising the importance of leveraging ChatGPT to enhance tourist trust and sustainable actions.