Astral Launches ty: A Rust-Powered Python Type Checker That Runs 10-60x Faster Than mypy

Astral, the company behind the uv Python package manager and the ruff Python linter, released ty (formerly codenamed Red-Knot) in beta on December 16, 2025, with a stable release targeted for 2026. ty is a Python type checker written in Rust that delivers 10-60x speed improvements over mypy, following the same playbook that made ruff and uv successful: rebuild a slow Python ecosystem tool in Rust.

Performance

Benchmarks on the home-assistant project (without caching) show ty completing type checking in 2.19 seconds, compared to 45.66 seconds for mypy and 19.62 seconds for Pyright. For incremental diagnostics via the Language Server Protocol (LSP) — the metric that most directly affects developer experience during active editing — ty completes analysis on the PyTorch project in 4.5 milliseconds, compared to 370.5 milliseconds for Pyright. The 80x improvement in incremental analysis means that type errors appear effectively instantaneously as a developer types, rather than after a noticeable delay.

The performance advantage holds across both cold (no cache) and warm (cached) scenarios, though the gap is most dramatic without caching — the scenario that affects CI pipelines, fresh clones, and first-time project setup. For large Python codebases where mypy type checking adds minutes to CI pipeline execution, ty's speed translates directly to shorter feedback loops and faster development cycles.

Type System Features

ty introduces first-class intersection types, a type system feature that mypy and Pyright do not natively support. Intersection types allow expressing that a value satisfies multiple type constraints simultaneously, which is useful for modeling complex API contracts. The type checker also includes sophisticated reachability analysis, which identifies code paths that can never be executed based on the type constraints in scope — helping developers find dead code that type-aware linting alone might miss.

Language Server

ty includes a full Language Server Protocol implementation with Go to Definition, Symbol Rename, Auto-Complete, and Auto-Import capabilities. This positions ty not just as a batch type checker for CI but as a comprehensive development environment backend. The combination of fast incremental type checking with LSP features means that ty can serve as the single backend for both real-time editor diagnostics and pre-commit/CI type validation, replacing both mypy (batch checking) and Pyright (LSP server) with a single tool.

The Astral Ecosystem

ty is the third major Python tool from Astral, following uv (package and project management) and ruff (linting and formatting). All three tools are written in Rust and deliver order-of-magnitude performance improvements over their Python-native predecessors. The pattern is consistent: identify a foundational Python development tool that is limited by Python's execution speed, rebuild it in Rust, and ship it as a drop-in replacement with dramatic performance gains.

The cumulative effect of uv, ruff, and ty is a Rust-powered Python development toolchain that handles package management, linting, formatting, and type checking — the four most computationally intensive parts of the Python development workflow — at speeds that were previously impossible with Python-native tools.