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Pylance now accepts Meta's Pyrefly as its type checker in VS Code

Microsoft announced the Type Server Protocol, an open standard that separates the Python extension from the type checker, and a partnership with Meta to use Pyrefly instead of Pyright.

By 3 min read
  • Python
  • VS Code
  • Microsoft
  • Meta

On October 21, 2026, Microsoft's Python blog introduced the Type Server Protocol (TSP), an open standard that extends the Language Server Protocol so editors and tools can use a type checker as a backend. In practice, Pylance keeps the IDE layer (completions, Quick Info, environment management and GitHub Copilot integration) while static analysis can come from another engine.

The first alternative engine is Pyrefly, Meta's type checker. Pyright stays the default, but you can switch from the status bar or with the Python › Analysis: Diagnostics Source setting, choosing "Pylance + Pyrefly". If the project already has Pyrefly installed or a pyrefly.toml, Pylance offers the switch on its own.

According to the post, it requires Pylance 2026.4.1 or newer and Pyrefly 0.60.0 or newer. Microsoft says Pyrefly checks 1.8 million lines per second. Feedback goes to the issues of the pylance-release repository on GitHub.

Original source: Microsoft Python Blog

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