Anthropic Releases Claude Fable 5, Its First Mythos-Class Model
2 min readAnthropic released Claude Fable 5 on June 9, and it is not just another model update. Fable 5 is the first member of a brand new “Mythos-class” tier that sits above Opus, the family that topped Anthropic’s lineup for the past two years. The company calls it the most capable model it has ever made generally available, and early benchmarks back that up.
A New Tier Above Opus
Until this week, Anthropic’s hierarchy was simple: Haiku for speed, Sonnet for balance, Opus at the top. The Mythos class changes that structure. Anthropic actually announced two models, Claude Fable 5 and Claude Mythos 5, which share the same underlying model but differ in their guardrails. Mythos 5 remains restricted to approved partners, including cybersecurity teams in the company’s Project Glasswing effort and select biology researchers.
What Anthropic Shipped
Fable 5 is the version the public gets, and its safeguards are the most interesting part of the launch. Instead of refusing risky requests outright, a classifier layer detects prompts touching cybersecurity, biology and chemistry, or model distillation and routes those sessions to Claude Opus 4.8, the previous flagship. According to TechCrunch, the fallback triggers in fewer than 5 percent of sessions.
The numbers are striking. Fable 5 posts 80.3 percent on SWE-Bench Pro, roughly 11 points ahead of the next best model, and carries a 1 million token context window. Pricing lands at $10 per million input tokens and $50 per million output tokens, double Opus 4.8, as CNBC reports. Subscribers on Pro, Max, Team, and Enterprise plans can use it at no extra cost through June 22, after which it moves to usage credits. It is also live on Amazon Bedrock and GitHub Copilot.
Why Claude Fable 5 Matters
This launch is a new playbook for frontier AI. Rather than holding back its strongest system or shipping a watered-down version, Anthropic released full Mythos-class capability with targeted fallbacks only where dual-use risk is highest. If the approach holds up, expect rivals to copy the two-track model strategy.
The next milestone is June 23, when Fable 5 shifts to credit-based access and real demand becomes visible. For now, the most powerful publicly available AI model has a new name.