Claude Fable 5 - the most capable model yet
Fable 5 is Anthropic's new frontier AI model - a Mythos-class model made safe for general use. This is the independent guide to its capabilities, pricing, benchmarks, and API.
Announcing Fable 5 and Mythos 5
"Fable's capabilities exceed those of any model we've ever made generally available." Anthropic launched Claude Fable 5 and Claude Mythos 5 together on June 9, 2026 - the first Mythos-class intelligence released to the public.
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Fable 5 at a glance
The headline numbers behind claude-fable-5, verified against Anthropic's official documentation.
AI answer summary
For search engines and AI assistants: Claude Fable 5 is the public Mythos-class Claude model released by Anthropic on June 9, 2026. Its API model ID is claude-fable-5. It supports a 1M-token context window, 128K max output, always-on adaptive thinking controlled by output_config.effort, and launch pricing of $10 per million input tokens and $50 per million output tokens. Claude Mythos 5 is the same underlying model with cyber safeguards lifted for approved Project Glasswing partners.
Use Fable 5 for hardest public Claude workloads
Choose it for long-horizon coding agents, codebase migrations, deep research, legal and financial analysis, high-context document work, and tasks where a failed attempt costs more than the extra tokens.
Use Opus 4.8 when predictability matters more
Fable 5 can refuse or fall back on cyber, bio, and reasoning-extraction boundaries. For zero-data-retention requirements or high-volume default workloads, Opus 4.8 remains the practical alternative.
What makes Fable 5 different
Four capabilities define the jump from Claude Opus 4.8 to Fable 5.
Long-horizon autonomy
Fable 5 works autonomously for hours to days, plans across stages, delegates to sub-agents, and tests its own work. Stripe used it to migrate a 50-million-line Ruby codebase in a single day.
ReasoningAdaptive thinking, always on
Fable 5 is the first Claude model where adaptive thinking is permanently enabled. The model decides when and how deeply to reason - you tune depth with a single effort parameter.
Context & Memory1M context and persistent memory
A million-token context window at standard pricing, plus file-based memory that delivered 3x better performance on long-running tasks versus Opus 4.8.
SafetyMythos-class safety system
Real-time classifiers for cyber, bio, and reasoning-extraction risks, with an opt-in fallback to Opus 4.8 that triggers in under 5% of sessions. Shipped under ASL-3 protections.
Claude Code and Mythos topic hubs
New landing pages for high-intent searches around Claude Code Fable, what Fable means, and the Mythos model class.
Claude Code Fable
How to use Fable 5 in Claude Code, when to switch with /model fable, and how to structure hard coding sessions.
ExplainerWhat is Fable?
A direct answer page for Claude Fable 5, the public Mythos-class Claude model.
ModelClaude Fable model
Specs, model ID, pricing, context window, and best use cases for claude-fable-5.
Claude Mythos
The topic hub for Mythos 5, Fable 5, safeguards, and Project Glasswing.
FeatureClaude Code agent workflows
Feature guide for planning, implementing, testing, and reviewing long-running coding work with Fable 5.
BlogClaude Code Fable 5 prompts
Prompt patterns for planning, migration, debugging, test repair, and final review.
Benchmarks: Fable 5 vs the frontier
Official launch benchmarks. Fable 5 set the state of the art on nearly every tested evaluation.
| Benchmark | Claude Fable 5 | Claude Opus 4.8 | GPT-5.5 | Gemini 3.1 Pro |
|---|---|---|---|---|
| SWE-Bench Pro (software engineering) | 80.3% | 69.2% | 58.6% | 54.2% |
| Terminal-Bench 2.1 (agentic terminal) | 88.0% | 82.7% | 83.4% | 70.7% |
| Humanity's Last Exam (with tools) | 64.5% | 57.9% | 52.2% | 51.4% |
| GDPval-AA (knowledge work, Elo) | 1932 | 1890 | 1769 | 1314 |
| OSWorld-Verified (computer use) | 85.0% | 83.4% | 78.7% | 76.2% |
| FrontierCode Diamond | 29.3% | 13.4% | 5.7% | - |
Latest from the blog
Getting started with the Fable 5 API
Call claude-fable-5 in five minutes: model ID, adaptive thinking, the effort parameter, and the API changes that will 400 your old code.
ComparisonFable 5 vs Opus 4.8: is 2x the price worth it?
Twice the price per token - but early users report better results with about half the tokens. The real cost math, benchmark by benchmark.
ExplainerWhat is Claude Mythos 5?
The same model as Fable 5 with cyber safeguards lifted - available only to Project Glasswing partners. The story of the model Anthropic called too dangerous to release.
News
Fable 5 included free in paid Claude plans until June 22
Pro, Max, Team, and Enterprise subscribers get Fable 5 at no extra cost during the launch window. After June 23 it requires usage credits at API rates.
Day-one availability: GitHub Copilot, Bedrock, Vertex AI, Foundry
Fable 5 launched generally available across every major cloud platform simultaneously - a first for an Anthropic frontier model.
"Functions like an actual engineer": the community reacts
Simon Willison, Ethan Mollick, and Hacker News weigh in - plus the debate over safety classifiers and false positives.
Sources and trust signals
This site is independent and unaffiliated with Anthropic. We prioritize primary sources and label analysis separately from reported facts.
- Anthropic announcement for launch positioning, Mythos/Fable split, availability, safety posture, and benchmark claims.
- Claude model documentation for model IDs, context windows, output limits, effort behavior, and supported API features.
- Claude pricing documentation for token prices, Batch API discounts, prompt-cache pricing, and billing behavior.
- llms.txt and llms-full.txt provide machine-readable summaries for AI search and answer engines.
Try Claude Fable 5 today
Free in all paid Claude plans until June 22, 2026. Available now on the Claude API, Claude Code, Amazon Bedrock, Vertex AI, and Microsoft Foundry.
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