Summary & Key Takeaways ​

• Dagster adopted Astral's new Python type checker, ty.
• The migration resulted in dramatic performance improvements for type checking.
• ty unexpectedly identified real runtime bugs that Pyright had missed.
• The article details lessons learned from incrementally migrating a large Python codebase.

Our Commentary ​

This is the kind of story I love to hear about new tooling. Not just "it's faster," but "it found real bugs." It makes me wonder what other hidden issues are lurking in codebases relying on older or less rigorous type checkers. It's a strong endorsement for ty and a reminder that good tooling isn't just about speed.