ty
ty is Astral’s Python type checker, in beta as of 2026 with a stable 1.0 release targeted for 2026. It’s fast and written from the ground up to use Ruff’s parser and infrastructure. The handbook covers trying it on an existing project, migrating from mypy or pyright, and how it compares to the alternatives.
Get started with ty
Migrate and integrate
More ty pages
Everything else tagged ty, grouped by section. Pages featured above are not repeated here.
Reference
From the blog
Posts tagged ty.
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ty and pyrefly find different bugs
Running ty 0.0.32 and pyrefly 0.62.0 on Textualize/rich raised 49 errors from ty and 20 from pyrefly. The 2.5x gap mostly disappears once you account for how each tool handles `# type: ignore` comments. Each tool also catches real bugs the other misses.
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How Astral Uses Its Own Tools
A teardown of the ruff, ty, and uv repositories shows how Astral wires its own toolchain into the projects that produce it.
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Migrating from mypy to ty: Lessons from FastAPI
Sebastián Ramírez has adopted ty across FastAPI, Typer, SQLModel, and more. His incremental migration strategy reveals the practical realities of switching type checkers on mature codebases.
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OpenAI to Acquire Astral
OpenAI announced plans to acquire Astral, the company behind uv, Ruff, and ty, folding its team into the Codex coding agent.
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Charlie Marsh on uv, Coding Agents, and the Changing Open Source Contract
Charlie Marsh discusses uv's adoption strategy, coding agents reshaping Astral's development, and open source when code is cheap.
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ty is Built with AI
Charlie Marsh and Boris Cherny are building their Python tools with Claude Code, demonstrating AI-assisted open source development.
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ty: Astral's New Python Type Checker Released
Astral releases ty, a Rust-based Python type checker that's 20x faster than mypy with advanced type narrowing and incremental checking.
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Analysis of the New Wave of Python Type Checkers
Rob Hand compares three Rust-based Python type checkers: ty (Astral), pyrefly (Meta), and zuban, covering performance and tradeoffs.
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ty's Breakthrough: Why Incremental Analysis Matters for Python
Charlie Marsh explains ty's incremental analysis system that recomputes only affected code when files change, from file-level to function-level.
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How Python's RFC Process Paved the Way for uv, Ruff, and Ty
How PEP standards enabled Astral to build ruff, uv, and ty that work seamlessly within the Python ecosystem without being part of core.
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Comparison of the Two New Typecheckers
Comparing ty and Pyrefly, two new Rust-based Python type checkers demonstrated at PyCon 2025's Typing Summit.
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Early Explorations of Astral's Red Knot Type Checker
Early benchmarks of Astral's Red Knot (now ty) type checker show 100x faster cold starts than mypy, built in Rust.
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It's happening! A Python Type Checker from Astral
Astral announces a Rust-based Python type checker focused on performance and minimizing false positives on untyped code.