model-safety

Anthropic is redeploying Claude Fable 5 after a month-long government-mandated takedown triggered by Amazon researchers discovering a method to bypass the model's cybersecurity safeguards. The returning version includes enhanced safety classifiers that automatically block cybersecurity tasks and revert to Opus 4.8, with restricted availability through usage credits only.

The US government forced Anthropic to withdraw its Fable 5 and Mythos 5 models, citing national security concerns after Amazon researchers allegedly discovered a method to bypass Fable 5's safety guardrails. Cybersecurity researchers have signed an open letter opposing the ban, with Anthropic noting similar vulnerabilities exist in competing models.

Anthropic released Claude Opus 4.8 on May 28, 2026, replacing Opus 4.7 at unchanged pricing. The company claims the model's misalignment rates match those of Claude Mythos Preview, the experimental model deemed too dangerous for public release in April 2026. Opus 4.8 delivers faster thinking modes at one-third the cost of version 4.7.

Anthropic has released Claude Opus 4.7, its most powerful generally available model, though it scores lower than the company's Mythos Preview model on every evaluation. The company intentionally reduced Opus 4.7's cybersecurity capabilities during training as it tests safety measures before releasing more powerful models.