Google dumps in-house Pytype for Meta's Rust-based Pyrefly, which checks 1.85M lines/sec
bigaiguy · x · 2026-10-31
Google has replaced its decade-old in-house Pytype with Meta's open-source Pyrefly (MIT, Rust). Pytype analyzed compiled bytecode and broke with every Python release; Python 3.12 is its final supported version.
Pyrefly highlights:
- Checks 1.85M+ lines/sec, 15x faster than Mypy/Pyright on PyTorch
- Passes 97% of Python's typing conformance suite
- Doubles as a language server; sub-10ms rechecks; VSCode/Neovim/Zed extensions
- Default checker for Instagram's 20M-line codebase; adopted by PyTorch and JAX
- Built-in Pydantic/Django/pytest support; migration via pyrefly init, suppress, infer
- Official GitHub Action for inline PR errors; installs via pip/conda/uv/poetry/pixi
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