# Anthropic loosens Fable 5's biology safeguards

> The AI company reduced false positives by 85% while still blocking dual-use research that could enable biological weapons.
- Title: Anthropic loosens Fable 5's biology safeguards · Anthropic
- Summary: The AI company reduced false positives by 85% while still blocking dual-use research that could enable biological weapons. Fable 5 now handles everyday…
- Keywords: anthropic, fable 5, claude, opus 5, ai safety, biology safeguards, safety classifiers, dual-use research, biological weapons, healthcare ai, drug development, jailbreaks
- Source: Anthropic — https://anthropic.com/news/improving-fable-5-s-biology-safeguards
- Read time: 2 min
- Topics: anthropic, fable 5, claude, opus 5, ai safety, biology safeguards, safety classifiers, dual-use research, biological weapons, healthcare ai, drug development, jailbreaks
## 85% fewer biology blocks
Anthropic updated Fable 5 to reduce false positives on biology questions. Users will see far fewer fallbacks to less capable models.
## Everyday health questions now work
Users can now get help interpreting lab results, understanding symptoms, and learning biology. Healthcare professionals get more clinical support.
## Professional research still blocked
Fable 5 still falls back to Opus 5 for dual-use requests like virology, toxicology, and molecular design. It's not yet usable for drug development.
## Why block biology at all
Fable 5 outperforms experts on complex biological tasks. In the wrong hands, those capabilities could help develop biological weapons.
## Hard to separate good from bad
Beneficial and harmful biology uses often look identical. Developing vaccines requires growing dangerous pathogens; hypertension drugs came from snake venom.

> It's often difficult to tell apart beneficial and harmful uses of AI in biology.
## Sophisticated actors hide intent
Malicious users know how to make dangerous tasks look like ordinary research. The US Intelligence Community warns that state actors maintain active bioweapons programs.
## Launched with everything blocked
Anthropic intentionally blocked almost all biology queries at launch. They accepted high false positives because misuse could be catastrophic.
## How safety classifiers work
Smaller AI systems detect when Fable 5 is asked to perform safeguarded biology tasks. When triggered, requests get rerouted to the less capable Opus 5.
## Classifiers are hard to tune
Classifiers must avoid false positives and false negatives while resisting jailbreak attempts. This requires extensive research and testing.
## Rewrote the classifier rules
Anthropic carefully rewrote the classifier's constitution to carve out benign uses in detail. They consulted internal and external experts on the changes.
## Safety margin still exists
Some low-risk requests still get blocked out of caution. The classifier now sits between clearly benign content and dual-use research.
## Trusted access coming
Anthropic is committed to developing safe pathways for researchers to access frontier biology capabilities. They're seeking ongoing feedback to improve safeguards.
## Key takeaway

Fable 5 now handles everyday health questions without blocking, but still restricts professional biology research that could be misused.