You've heard about Python type annotations, but wondered if they're useful in the real world? Worried you've got too much code and can't afford to annotate it? Type-checked Python is here, it's for real, and it can help you catch bugs and make your code easier to understand. Come learn from our experience gradually typing a million-LOC production Python application! Type checking solves real world problems in production Python systems. We'll cover the benefits, how type checking in Python works, how to introduce it gradually and sustainably in a production Python application, and how to measure success and avoid common pitfalls. We'll even demonstrate how modern Python typechecking goes hand-in-hand with duck-typing! Join us for a deep dive into type-checked Python in the real world.