01What Is Claude Fable 5?

Claude Fable 5 is a new AI model from Anthropic, released on June 9. It is the first model in the Mythos class that is safe for general use. The Mythos class was previously only available to vetted partners in Project Glasswing.

Fable 5 is the same as Mythos 5 but with safety guardrails.

This model is designed for complex, long-horizon tasks. It is better than any model ever released by Claude, with state-of-the-art performance on many benchmarks. It excels in software engineering, knowledge work, vision, and scientific research.

The longer the task, the bigger the lead Fable 5 has over other models.

02Key Features and Announcements

Claude Fable 5 introduces a brand-new model class, Mythos, which sits above the previous classes like Haiku, Sonnet, and Opus. It has a million-token context window and 28k max output per request. For long context retrieval, it scores 79.4, compared to Opus 4.8's 68.4.

  • First model to break 90% on Hexys Core Analytics Benchmark.
  • Can play Pokemon FireRed using vision alone, without special harnesses.
  • Anthropic's internal experts improved research results with Fable 5, running novel research autonomously for a week.
  • Biologists preferred its molecular hypotheses 80% of the time over Opus models in blind tests.
  • Stripe used it for a migration of a 50-million-line codebase, compressing months of engineering into days.

These features make Fable 5 a powerful tool for anyone building apps, websites, or doing research. It is designed to handle tasks that require long-running, complex reasoning.

03How to Set Up Claude Fable 5

Setting up Claude Fable 5 is simple. On the Claude API, it is fully available today. For subscription plans, it is included on Pro Max, Team, and seat-based enterprise plans at no extra cost until June 22.

After that, you will need usage credits.

  1. Visit the Claude API or your Claude subscription plan (Pro Max, Team, or Enterprise).
  2. Select Fable 5 as your model in the API or in your chat interface.
  3. If you are a developer, integrate the API into your app or agent system.
  4. For agents, plug Fable 5 into an agent operating system like the AI Profit Boardroom to utilize its full power.
  5. Start with a simple task to test its capabilities before scaling up.

If capacity allows, Anthropic may extend the included window. They aim to restore Fable 5 after June 22, but the timeline is uncertain. So start using it now to explore its features.

04How to Use Claude Fable 5 Effectively

Fable 5 can be used in many ways. In the episode, Julian showed how he plugged it into his agent operating system. He created an example guide about Claude Fable 5 and Mythos 5, fully generated by the model.

It researched, took quotes, and organized images using the chat PPT image API. You can also use Fable 5 to build tools like an invoice generator or even a website with interactive animations.

  • Use it for coding tasks like building apps, games, tools, and websites.
  • For knowledge work, use it to research topics, gather sources, and create organized guides or reports.
  • Set up an agent operating system to have Fable 5 work with other agents like Hermes, Gemini, and Codex, all sharing memory.
  • Use the AI agent mastermind system to brainstorm ideas with Fable 5 and other models, then implement them.

To get the most out of Fable 5, avoid using it in a lonely chat tab. Instead, integrate it into a system that saves all outputs, allows multiple agents, and provides shared context. This way, you avoid re-explaining your business and keep everything organized.

05Benchmarks and Comparisons with Opus

Fable 5 shows big jumps over Opus 4.8. On WE Bench verified, it scores 95% compared to Opus's 88.6%. On SWE Bench Pro, Fable 5 scores 80%, Opus 69%, and GPT 5.5 scores 58.6%.

For Frontier Code, Fable 5 scores 29.3, more than double Opus's 13.4.

On long context retrieval, Fable 5 scores 79.4 versus Opus 68.4. In tool use marathon, Fable 5 scored 61.7% in 19.8 average turns, while Opus scored 59.9% in 24.5 turns. This means Fable 5 gets better results in fewer steps, which could mean cheaper agent runs in theory.

However, the API cost is much higher, so check the pricing before scaling.

The model is better than any previously available, as noted by Stripe CEO and Scott Wu of Cognition. These results show that Fable 5 is a significant step up in performance.

06Tips, Limits, and Mistakes to Avoid

Most people will waste Fable 5's potential by using it in a simple chat tab. That is like putting a Ferrari in a parking garage. You need a system around it to use it fully.

Avoid re-explaining your business each time; use an agent operating system that remembers your context.

  • Use the million-token context window to give the model large amounts of information at once.
  • Take advantage of the 28k max output for long reports or code files.
  • Be aware of the high API cost—test with small tasks first.
  • Watch the availability window: free until June 22, then requires credits.

Also, note the safety concerns. Anthropic issued a warning about AI self-improvement, but released Fable 5 anyway. This means you should use it responsibly.

Finally, don't forget to organize your outputs—use a workspace or dashboard to keep everything in one place.

07Who Should Use Claude Fable 5?

Claude Fable 5 is for developers, researchers, and creators who need high-level AI capabilities. It is especially useful for software engineers building apps, tools, or websites. Knowledge workers will benefit from its research and report generation features.

Scientists can use it for novel hypotheses.

Businesses like Stripe have used it for massive code migrations, showing its power in real-world scenarios. If you are an AI enthusiast, you can use it to build your own tools and systems. With the right setup, it can save you hours and produce better results than previous models.

Whether you are a beginner or an expert, Fable 5 can elevate your work, but you need to set it up correctly to see the full benefits.