Harvard’s CS50 course draws an explicit line in its official policy on AI tools: “In CS50, we do not allow the use of ChatGPT,” but the course’s own tutor at cs50.ai is permitted. The distinction is by design. CS50’s tool, nicknamed the Duck, is described as built “to behave more like a good tutor, leading students toward answers rather than spoiling them outright,” whereas a general chatbot will readily produce a finished solution. The rule captures a stance many schools and employers later adopted: sanction a purpose-built, constrained assistant while restricting general-purpose ones.