Pyrefly vs. Ty: Comparing Python's Two New Rust-Based Type Checkers

Note: I like using em-dashes while writing! Don’t worry, this is not written by AI. (context) Earlier this month, two new Rust-based Python type checkers hit the spotlight: pyrefly and ty. Although neither is officially released, they are a welcome change to the Python type checking world, historically dominated by mypy and pylance. While both are open-source and publicly downloadable for quite some time, there have not been any official announcements by Meta nor Astral on their brand new next-generation Python type checkers — until last week. At PyCon 2025, nestled away in a quiet Room 319 at the Typing Summit, we had our first official sneak peek into both of these tools — the team behind them, their goals, visions, and ambitions — and their unique approaches to tackling Python’s typing problems. ty team presenting at the typing summit This blog is a collection of rough notes scribbled during the event, personal conversations with the team, and not-too-thorough experiments that ... Read full article.