Fable 5Anthropic's most powerful AI model.

Fable 5 (API model ID claude-fable-5, often written Fable5) is the most powerful AI model Anthropic has ever released. Launched in 2026, the Fable 5 model opens a new intelligence tier that sits above the Claude Opus family — the first of Anthropic's Mythos-class models to be generally available. Where earlier Claude models were tuned for either speed or depth, Fable 5 is built for the hardest problems: long-horizon agentic work, complex reasoning, large-scale code understanding, and enterprise-grade document analysis.

On specs, the Fable 5 model ships with a 1 million token context window — roughly 700,000 English words, or an entire codebase — and can produce up to 128K tokens of output in a single request. Thinking is always on: Fable 5 decides for itself when and how deeply to reason, with no manual thinking budgets to configure. Developers control depth through a simple effort parameter instead. The model also introduces a new tokenizer and a refreshed safety system, so prompts and token counts from older Claude models should be re-baselined.

Fable 5 pricing is straightforward: Anthropic charges $10 per million input tokens and $50 per million output tokens through the API — exactly double Claude Opus 4.8. There is no long-context premium; the full 1M window costs standard rates. If you just want to try the model without an API key, our playground sells one-time credit packs from $9.90, and new accounts get free credits on sign-up. See the full Fable 5 price breakdown on our pricing page.

How does Fable 5 compare with Claude Opus 4.8? The two models share the same API surface — adaptive thinking, no sampling parameters — but Fable 5 raises the ceiling on reasoning, coding, and agentic benchmarks, and is the better choice when output quality matters more than cost. Opus 4.8 remains the value pick for high-volume production traffic. Our detailed Fable 5 vs Opus 4.8 comparison covers pricing, context, thinking behavior, and when to choose each model.

The fastest way to understand what Fable 5 can do is to talk to it. Our online playground now runs Fable 5 right in your browser — alongside other leading models and OpenRouter Fusion — with no API key, no credit card, and free credits when you sign up. You can also put it to work immediately with our one-click AI tools: optimize a prompt, translate and polish text, or summarize a long document.