Anthropic built the Claude Fable 5 curbs to keep China’s AI labs out of its most powerful public model. The loudest complaints came from its own side of the firewall.
On 9 June, Anthropic released Claude Fable 5, a tamed, public-facing version of Mythos, the model it had withheld since April over its talent for finding and exploiting security flaws.
Fable 5, the company said, was “safe for general use.” Built into it was a set of classifiers that flag requests touching cybersecurity, biology, chemistry, distillation and frontier model development, then quietly route them to Anthropic’s second-best model, Claude Opus 4.8.
The word that caused the trouble was “quietly.” According to Anthropic’s own system card, the interventions limiting “frontier LLM development” would “not be visible to the user.” AI researchers said they were being silently downgraded, or shadowbanned, the moment Fable 5 decided their machine-learning work looked too much like an attempt to build a rival.
“It felt like Anthropic was saying to the public, we don’t trust anybody else to do AI research,” Will Brown, research lead at Prime Intellect, told Wired. The research firm SemiAnalysis said the model was degrading its GPU-inference work.
