Claude Fable 5
Anthropic's first Mythos-class model, tuned for the hardest coding benchmarks
Claude Fable 5 is a public, safety-restricted release of Mythos, an internal Anthropic model class that the company unveiled in April 2026 and initially withheld from general availability because of its advanced cybersecurity capabilities. Anthropic made Fable 5 available to enterprise customers and paid subscribers on June 9, 2026, after adding safeguards that redirect queries in high-risk areas like cybersecurity and biology to Claude Opus 4.8 instead, a mechanism the company says triggers in under 5 percent of sessions. On paper it is the strongest model Anthropic has shipped publicly: 95.0 percent on SWE-bench Verified, 80.3 percent on the harder SWE-bench Pro, and 92.6 percent on GPQA Diamond, with strong results in vision and scientific research tasks as well. It carries a 1 million token context window and is priced at $10 per million input tokens and $50 per million output tokens, double what Anthropic charges for Opus 4.8, reflecting its positioning as a specialty top-tier option rather than a general daily driver.