code-generation long-context autonomous-agents vision-models benchmarks

Claude Fable 5 launches with state-of-the-art benchmarks

Mythos-class model achieves strongest long-context reasoning and autonomous task execution; priced at $10/$50 per million tokens, half the cost of Mythos Preview.

June 10, 2026

Summary

Developers can now delegate multi-day codebase migrations and complex analytical tasks to a single model with improved token efficiency and vision capabilities. Extended context window (millions of tokens) with persistent memory enables autonomous agents to maintain state and self-correct across longer workflows.

Why it matters

Implementation verdict

Replaces Opus 4.8 for code generation, knowledge work, and vision tasks—available now at public pricing. Requires updating inference clients to handle extended context and autonomous loops. Worth adopting immediately for long-horizon coding tasks (50M-line migrations tested); vision-only mode replaces scaffolded harnesses. Mythos 5 (unrestricted version) limited to trusted access program initially.

Sources

1.Fable 5 compressed months of engineering into days
2.the model performed a codebase-wide migration in a day that would otherwise have taken a whole team over two months by hand
3.safeguards trigger, on average, in less than 5% of sessions
4.Fable 5 can work autonomously for longer than any previous Claude models
5.Fable 5 improved its outputs using its own notes
6.$10 per million input tokens and $50 per million output tokens—less than half the price of Claude Mythos Preview

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