You've used ChatGPT. You've probably been amazed, and maybe a little unsettled, by what it can do. But what is actually happening when you hit send? In this talk, Todd Hendry (Whitman '00, Partner Software Engineer at Microsoft) pulls back the curtain on large language models, explaining how they are trained on vast corpora of text, what "learning" actually means mathematically, and why building and evaluating these systems at scale is harder than it looks. We will touch on the core ideas, including transformers, loss functions, and reinforcement learning from human feedback, without requiring anything beyond calculus and curiosity. Todd will share what it is like to work at the intersection of Microsoft and OpenAI, along with the kinds of problems that researchers and engineers are actively working on.