Google moves from Pytype to Pyrefly for Python type checking

Google replaced its in-house Python type checker Pytype with Pyrefly, which uses static source-code analysis. Incremental rebuilds got up to 98% faster, critical-path times dropped over 90%, and compute hardware costs fell more than 80%.

• Pytype relied on bytecode analysis, slowing builds as the codebase grew
• Pyrefly speeds up incremental rebuilds by up to 98%
• Critical-path times dropped by more than 90%
• Compute hardware savings exceeded 80%