Frontier AI models such as Anthropic Mythos and OpenAI GPT 5.5 Cyber represent a paradigm shift in security testing by leveraging multi-step reasoning to chain vulnerabilities and misconfigurations into viable attack paths. Zscaler's evaluation demonstrates that these models significantly outperform legacy tools in speed and accuracy when embedded in structured testing harnesses, though they require careful contextual grounding to avoid severity inflation or pattern anchoring. Organizations are advised to implement Zero Trust architectures and deception technologies to mitigate the accelerated threat posed by AI-enabled adversaries.