Anthropic released Claude Fable 5, its most powerful publicly available AI model, bridging the gap between frontier capability and safety. Following a restricted rollout through Project Glasswing, the company now offers Fable 5 to all users, while Claude Mythos 5 remains accessible only to vetted partners in cybersecurity and biology.
A Model for the Masses with Built-in Restrictions
Fable 5 shares the same core architecture as Mythos but includes automatic guardrails that detect high-risk requests. When a prompt involves cybersecurity, biology, chemistry, or model distillation, the system reroutes it to Claude Opus 4.8. Anthropic reports that over 95% of sessions run fully on Fable 5 without fallback. The model is priced at $10 per million input tokens and $50 per million output tokens, making it the most expensive general-purpose model on the market.
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Record-Breaking Coding Performance
Benchmarks showcase Fable 5's strength. On SWE-bench Pro, it scores 80.3%, far ahead of GPT-5.5 at 58.6%. Stripe used Fable 5 to complete a codebase-wide migration in one day, a task that would have taken a team over two months manually. On FrontierCode Diamond, Fable 5 achieves 29.3% versus 13.4% for Claude Opus 4.8. Long-horizon autonomous coding is where the model excels, enabling enterprises to delegate complex software engineering projects.
Safety, Data Retention, and Enterprise Implications
Mythos 5 lifts some restrictions for trusted users, offering full capability in sensitive areas. Both models now require 30-day data retention, a policy Anthropic says is necessary for monitoring misuse. For regulated industries, this tradeoff between capability and data control will be a critical factor. The launch sets a precedent for how frontier AI labs can commercialize powerful models while gating dangerous capabilities. Enterprises must decide whether the gain in autonomous work justifies the new data governance requirements.
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For more on cybersecurity risks, see our coverage of Critical Linux Bug and Tchap Breach.
