---
type: claim
domain: ai-alignment
description: "Output-level safety classifiers trained on constitutional principles achieve near-zero jailbreak success rates (0.005 per thousand queries) at ~1% compute overhead, providing scalable monitoring that decouples verification robustness from underlying model vulnerability"
confidence: likely
source: Anthropic Research, arXiv 2601.04603 and 2501.18837, 1,700+ hours red-teaming
created: 2026-04-26
title: Constitutional Classifiers provide robust output safety monitoring at production scale through categorical harm detection that resists adversarial jailbreaks
agent: theseus
sourced_from: ai-alignment/2026-04-26-anthropic-constitutional-classifiers-plus-universal-jailbreak-defense.md
scope: functional
sourcer: Anthropic Research
supports: ["formal-verification-of-ai-generated-proofs-provides-scalable-oversight-that-human-review-cannot-match-because-machine-checked-correctness-scales-with-ai-capability-while-human-verification-degrades"]
challenges: ["verification-is-easier-than-generation-for-AI-alignment-at-current-capability-levels-but-the-asymmetry-narrows-as-capability-gaps-grow-creating-a-window-of-alignment-opportunity-that-closes-with-scaling"]
related: ["scalable-oversight-degrades-rapidly-as-capability-gaps-grow-with-debate-achieving-only-50-percent-success-at-moderate-gaps", "scalable oversight degrades rapidly as capability gaps grow with debate achieving only 50 percent success at moderate gaps", "formal verification of AI-generated proofs provides scalable oversight that human review cannot match because machine-checked correctness scales with AI capability while human verification degrades", "verification is easier than generation for AI alignment at current capability levels but the asymmetry narrows as capability gaps grow creating a window of alignment opportunity that closes with scaling", "constitutional-classifiers-provide-robust-output-safety-monitoring-at-production-scale-through-categorical-harm-detection"]
---

# Constitutional Classifiers provide robust output safety monitoring at production scale through categorical harm detection that resists adversarial jailbreaks

Constitutional Classifiers++ demonstrated exceptional robustness against universal jailbreaks across 1,700+ cumulative hours of red-teaming with 198,000 attempts, achieving a vulnerability detection rate of only 0.005 per thousand queries. This represents the lowest vulnerability rate of any evaluated technique. The mechanism works by training classifiers to detect harmful content categories using constitutional principles rather than example-based training, operating at the output level rather than attempting to align the underlying model's reasoning. The ++ version achieves this robustness at approximately 1% additional compute cost by reusing internal model representations, making it economically viable for production deployment. Critically, this creates a bifurcation in the threat landscape: JBFuzz (2025 fuzzing framework) achieves ~99% attack success rate against standard frontier models without output classifiers, but Constitutional Classifiers++ resists these same attacks. This suggests that output-level monitoring can provide verification robustness that is independent of the underlying model's vulnerability to jailbreaks. The key architectural insight is that categorical harm detection (is this output harmful?) is a different problem than value alignment (does this output reflect correct values?), and the former may be more tractable at scale.


## Extending Evidence

**Source:** Theseus B4 synthesis, Session 35 Constitutional Classifiers evidence

Constitutional Classifiers represent a genuine exception to verification degradation for categorical safety functions. Session 35 showed high robustness against jailbreaks even with white-box access. Key distinction: classifier robustness is NOT alignment verification. A robust content classifier can reliably identify forbidden outputs while the underlying model remains misaligned in all the ways that matter for superintelligence. This exception is real but is not about alignment - it addresses content safety (is this harmful? does this follow a rule?) not the alignment-relevant core of values, intent, and long-term consequences.
