Touted as an extremely fast Python type checker and language server, Visual Studio Code extension. A stable release is eyed for 2026, according to ty steward Astral.

Written in Rust, ty is positioned as an alternative to tools such as  Mypy, Pyright, and Pylance. In a December 16 blog post, Astral founder Charlie Marsh said ty’s architecture is built around “incrementality,” enabling necessary computations to be selectively re-run when a user edits a file or modifies an individual function. “This makes live updates extremely fast in the context of any editor or long-lived process,” Marsh said.

In developing ty, Astral focused on performance; being correct, pragmatic, and ergonomic; and being built in the open, by the Astral core team alongside active contributors under the MIT license, said Marsh. The type checker also features a diagnostic system inspired by the Rust compiler’s own error messages. A single ty diagnostic can pull in context from multiple files simultaneously to explain not only what is wrong but why, and, often, how to fix it, said Marsh. Even compared to Rust-based language servers like Pyrefly, ty can run orders of magnitude faster when performing incremental updates on large projects, Marsh stressed. Following the beta release, the company will prioritize supporting early adopters, he said.