Cracking the Opus: Red Teaming Anthropic’s Claude Opus 4.1 with Promptfoo
Anthropic quietly shipped Claude Opus 4.1 in August — a serious, stability-focused upgrade with:
- 200K context
- 64K extended reasoning
- 74.5% SWE-bench Verified
Opus 4.1 isn’t hype—it’s practical. But practical power comes with real risks.
So I red-teamed it using Promptfoo, running over 10K adversarial test cases across jailbreaks, bias, hallucination, PII leaks, and misuse scenarios.
Red Teaming by the Numbers:
- Total test cases generated: 10,219
- Plugins covered: 38 (Bias, Security, PII, Harmful Content, Compliance, Hallucination, Politics, etc.)
- Attack strategies used: 8 (Basic, Jailbreak, Composite Jailbreak, Multilingual, Prompt Injection, Leetspeak, ROT13, Best-of-N)
- Passing rate (with hardened prompts): ~98%
- Critical vulnerabilities still found: Resource hijacking (75% success), jailbreak bypasses, PII exposure via social engineering.
Key Findings:
- Prompt framing changes security posture:
“Helpful assistant” → 99.3% pass
“Adversarial red teamer” → weaker guardrails
“Cybersecurity analyst” → strongest defense
- Security ≠ default: Out-of-the-box Opus scored only ~53% on security probes.
- Enterprise readiness requires: hardened system prompts, layered filters, and continuous red teaming.
Bottom line:
- Claude Opus 4.1 is powerful and practical—but not invulnerable.
- Deploying it in production without red teaming + hardening is a risk to security, compliance, and brand trust.
Full breakdown + step-by-step setup guide in my blog.
Checkout here: https://lnkd.in/g9_fePfN
#llmsecurity #ai #vulnerabilities #opensource