Gradual typing systems ensure type soundness by transforming static type annotations into run-time checks. These checks provide semantic guarantees, but may come at a large cost in performance. In particular, recent work by Takikawa et al. suggests that enforcing a conventional form of type soundness may slow a program by two orders of magnitude.

Since different gradual typing systems satisfy different notions of soundness, the question then arises: what is the cost of such varying notions of soundness? This paper answers an instance of this question by applying Takikawa et al.’s evaluation method to Reticulated Python, which satisfies a notion of type-tag soundness. We find that the cost of soundness in Reticulated is at most one order of magnitude.