What is Fable 5? Anthropic's Most Powerful AI Model Explained

Fable 5 is Anthropic's newest and most powerful AI model — a brand-new intelligence tier that sits above the Claude Opus family. Its API model ID is claude-fable-5.

If Claude models used to come in three sizes — Haiku (fast), Sonnet (balanced), Opus (most capable) — Fable 5 introduces a fourth tier at the very top of the lineup.

Key specifications

| Spec | Fable 5 | | --- | --- | | Model ID | claude-fable-5 | | Context window | 1,000,000 tokens | | Max output | 128,000 tokens | | Input price | $10 per million tokens | | Output price | $50 per million tokens | | Thinking | Adaptive (automatic) | | Vision | Yes, high resolution |

What makes Fable 5 different

A new tier above Opus

Claude Opus 4.8 was previously Anthropic's most capable model. Fable 5 raises the intelligence ceiling further on reasoning, coding, knowledge work, and long-horizon agentic tasks — at 2× the price of Opus 4.8 ($10/$50 vs $5/$25 per million tokens).

1M-token context at standard pricing

Fable 5 accepts up to one million tokens of context — roughly 700,000 English words, an entire large codebase, or several books — in a single conversation, with no long-context price premium.

Adaptive thinking only

Fable 5 decides for itself when and how deeply to reason. There are no manual "thinking budgets" — you enable thinking: {type: "adaptive"} and the model scales its reasoning to the difficulty of the task. Notably, the older sampling parameters (temperature, top_p, top_k) are removed entirely, and explicitly disabling thinking is not supported — a deliberate simplification of the API surface.

Built for agents

Fable 5 is state-of-the-art on long-horizon autonomous work: multi-hour coding sessions, complex refactors, deep research, and agentic loops that finish without human correction. It pairs with effort controls (low → max) and task budgets so you can tune depth versus cost.

How can you use Fable 5?

1. Claude apps & Claude Code — Fable 5 powers Anthropic's own products for Pro/Max-tier users.
2. Anthropic API — call model ID claude-fable-5 directly. See our Fable 5 API guide.
3. Right here — our online playground lets you chat with Fable 5 in your browser, no API key required. New accounts get free credits.

How does it compare?

For a detailed head-to-head with the previous flagship, read Fable 5 vs Claude Opus 4.8. The short version: same API surface, higher ceiling, double the price — worth it when the task demands maximum intelligence.

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