We present Korbit, a large-scale, open-domain, mixed-interface,
dialogue-based intelligent tutoring system (ITS). Korbit uses machine learning,
natural language processing and reinforcement learning to provide interactive,
personalized learning online. Korbit has been designed to easily scale to
thousands of subjects, by automating, standardizing and simplifying the content
creation process. Unlike other ITS, a teacher can develop new learning modules
for Korbit in a matter of hours. To facilitate learning across a widerange of
STEM subjects, Korbit uses a mixed-interface, which includes videos,
interactive dialogue-based exercises, question-answering, conceptual diagrams,
mathematical exercises and gamification elements. Korbit has been built to
scale to millions of students, by utilizing a state-of-the-art cloud-based
micro-service architecture. Korbit launched its first course in 2019 on machine
learning, and since then over 7,000 students have enrolled. Although Korbit was
designed to be open-domain and highly scalable, A/B testing experiments with
real-world students demonstrate that both student learning outcomes and student
motivation are substantially improved compared to typical online courses