Claude Fable 5 and Mythos 5: what Anthropic launched

Anthropic has released Claude Fable 5, a new Claude model for hard knowledge work, coding, documents, vision tasks and long-running agent workflows. It is not a separate app, but a new model inside the Claude ecosystem.

The company also introduced Claude Mythos 5. It uses the same underlying model, but access is limited to vetted Project Glasswing partners and selected researchers. For most users, the main release is Fable 5.

What happened

On June 9, 2026, Anthropic announced Claude Fable 5 as a generally available Mythos-class model. The company says Fable 5 is strongest on longer and more complex tasks: software engineering, knowledge work, document analysis, vision and scientific workflows.

Anthropic's model docs list Fable 5 as available on the Claude API, Claude Platform on AWS, Amazon Bedrock, Google Vertex AI and Microsoft Foundry. The API model ID is claude-fable-5.

How Fable 5 is different

Fable 5 is less about quick answers and more about sustained work. Anthropic positions it for large code migrations, complex implementations, multi-stage analysis, tables, diagrams, PDFs and checking outputs against visual goals.

For software work, it makes the most sense alongside Claude Code. In an agent harness, it can plan stages, delegate subtasks and validate its own work. That makes it closer to a senior project assistant than a simple drafting chatbot.

What Mythos 5 is

Claude Mythos 5 is the restricted version of the same underlying model for dual-use domains. Anthropic focuses on cybersecurity and biology research. Access is limited to vetted partners and will expand through trusted access programs.

The Project Glasswing context matters. In May, Anthropic said roughly 50 partners had used Claude Mythos Preview to find more than 10,000 high- or critical-severity vulnerabilities. In June, the program expanded to about 150 organizations across more than 15 countries.

Safeguards

Fable 5 is broadly available, but with safeguards. If a request is flagged as cybersecurity, biology, chemistry or distillation-related, the response may be handled by Claude Opus 4.8 instead. Anthropic says more than 95% of Fable sessions do not trigger this fallback.

That is the useful way to read the release: Fable 5 is a stronger model, but Anthropic is trying to release it with stricter controls in areas where capability can create risk.

Access and pricing

• Claude Fable 5 became available on June 9, 2026.
• The API model ID is claude-fable-5.
• Pricing is $10 per million input tokens and $50 per million output tokens.
• From June 9 through June 22, Fable 5 is included on Pro, Max, Team and seat-based Enterprise plans at no extra cost.
• Starting June 23, Anthropic plans to require usage credits for Fable 5 on subscriptions until capacity improves.
• Fable 5 and Mythos 5 require 30-day data retention for safety monitoring.

Who should try it

Fable 5 is most interesting if you have hit the limits of normal chat models: large coding tasks, difficult documents, financial analysis, legal review, research projects or interface prototyping from screenshots. For simple everyday prompts, it may be more model than you need.

For easier tasks, other Claude models may be enough. For coding, start with Claude plus Claude Code and keep tests, code review and change control in human hands.

Sources

This article is based on Anthropic's official Claude Fable 5 and Claude Mythos 5 announcement, the Claude Fable 5 page, the Claude Mythos 5 page, the Claude model documentation, and Anthropic's Project Glasswing initial update and expansion note.