When AI Becomes the Attacker: A Defense Playbook for the Autonomous Exploit Era

In March 2026, two benchmarks dropped that should keep every DeFi developer awake at night. OpenAI and Paradigm's EVMbench showed GPT-5.3-Codex successfully exploiting 72.2% of historical Ethereum vulnerabilities. Anthropic's SCONE-bench found that over half of 2025's real-world blockchain exploits could be replicated autonomously by current AI agents - no human hacker required. Meanwhile, Anthropic's "Mythos" security model was accidentally leaked on March 28, 2026, through a CMS misconfiguration. A model specifically trained to detect smart contract vulnerabilities is now in the wild.