Microsoft opens Pylance to alternative Python type checkers
Microsoft introduced the Type Server Protocol (TSP), an open protocol that lets editor tools request type information from interchangeable Python checkers. Pylance can now use Meta’s Pyrefly while retaining its editor features; Pyright remains the default. The change separates type analysis from IDE integration, giving developers another checker choice without switching away from Pylance.
Microsoft for Python Developers Blog · Oct 21, 2026
Why it matters
Python teams can try a different checker inside their existing editor workflow, while tool builders get a defined interface for type queries.
More context
TSP extends Language Server Protocol conventions and exposes requests for types, import resolution and search paths. The Microsoft announcement says Pylance needs version 2026.4.1 or newer for Pyrefly support. The protocol specification is still in its 0.x series, where minor versions may introduce breaking changes.
Keep in mind
The announcement and performance claims are from Microsoft and Meta. TSP is new, and the protocol documentation says 0.x minor versions may break compatibility.
Original read