This examination by Nelson Elhage investigates the performance of CPython's new tail-calling interpreter, finding that initial reports of 10-15% speedups were significantly inflated due to an unrelated LLVM 19 compiler regression affecting the comparison baseline. When benchmarked against properly optimized older versions or compilers, the actual performance gain attributable to the new interpreter implementation itself is more modest, typically in the 1-5% range.
https://blog.nelhage.com/post/cpython-tail-call/