Most testing strategies miss rare edge cases until customers find them in production. Our system automatically generates targeted unit tests for rare bugs, including the one that would have caught Anthropic’s recent approximate top-K bug. In this blog post, we’ll provide a brief overview of how it works. Figure 1: Unit-level PBTs are fast but miss edge cases. Proofs offer exhaustive coverage but require extensive reasoning and code refactoring. End-to-end PBTs have coverage but are not compute e...