Anthropic Introduces Claude Fable 5 and Claude Mythos 5

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Anthropic has released Claude Fable 5 and Claude Mythos 5, two Mythos-class AI models. Fable 5 is tailored for general use with conservative safety fallbacks, whereas Mythos 5 provides unrestricted access to advanced cybersecurity capabilities for vetted defenders via Project Glasswing.

Key points

  1. Fable 5 and Mythos 5 share the same underlying architecture; Fable 5 routes sensitive queries to Claude Opus 4.8 (triggering in under 5% of sessions on average).
  2. Mythos 5 is initially deployed through Project Glasswing in collaboration with the US government for cybersecurity and critical infrastructure defence.
  3. API pricing is set at $10 per million input tokens and $50 per million output tokens, cutting Claude Mythos Preview costs by more than half.
  4. Early testing at Stripe showed a 50-million-line Ruby codebase migration completed in a single day, compared to an estimated two months of manual team work.
  5. The model achieved top scores on Cognition's FrontierCode benchmark and demonstrated vision capabilities such as rebuilding web app code solely from screenshots.
  6. Mythos 5 accelerated drug design processes tenfold and independently trained high-performing genomics machine learning models.

Why it matters

The transition to Mythos-class models represents a marked improvement in autonomous, long-horizon task execution. Engineering teams can delegate large-scale code refactorings, multi-agent workflows, and complex research analyses with higher token efficiency and less manual supervision.

Analysis

Anthropic employs a dual-release strategy to manage extreme capability risks. By isolating unrestrained cybersecurity and biological reasoning to trusted partners in Project Glasswing while offering Fable 5 with automatic fallbacks to Opus 4.8, the company attempts to lower risk without blocking broad enterprise adoption. The halved pricing also signals increased inference efficiency.

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Summary generated by AI (Gemini 3.8 Flash, 27 September 2026). It may contain errors – the original source is authoritative.

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