OpenAI's Codex Security replaces traditional static analysis (SAST) with AI-driven validation, targeting vulnerabilities where code checks appear sufficient but fail in practice. The system starts with the repository's architecture and intended behavior, validating constraints before human review. This approach addresses SAST's core limitation: tracing data flow from source to sink doesn't prove the check actually constrains the value post-transformation.

For instance, a regex validation followed by URL decoding might pass SAST but fail in a real redirect handler due to encoding ambiguities. Codex Security isolates transformation pipelines, using techniques like micro-fuzzing and z3-solver to falsify invariants, ensuring issues are proven before human triage. This reduces false positives and focuses on real-world vulnerabilities.