Anthropic releases Claude Fable 5.2 and Mythos 5.2, pairing record-high benchmarks with 20% API cost reduction

What happened

Anthropic released Claude Fable 5.2 and Mythos 5.2 on November 9, 2026 — the company's first frontier models after nearly four months offline due to regulatory negotiations with the White House. Fable 5.2 is generally available; Mythos 5.2 is restricted to vetted organizations.

Context and impact

The releases arrive just ahead of Anthropic's IPO roadshow. Fable 5.2 sets new records on FrontierCode 2.0, and a 1,000-agent run formalized Fermat's Last Theorem in 30 hours. Over 90% of commits to Anthropic's own codebase are now written by Claude — raising recursive self-improvement (RSI) concerns that the company addressed directly in the system card.

Details

• Pricing: $8 / 1M input, $40 / 1M output tokens
• Fast mode (2.5x faster): $16 input / $80 output
• FrontierCode 2.0 (xhigh): 49.1% — highest score of any released model
• Remote Labor Index: 41.3% vs. 21.3% for Opus 5.5
• Humanity's Last Exam (with tools): 74.2%
• Anthropic deliberately limited kernel-optimization and LLM-architecture capabilities to slow potential RSI
• Zero Data Retention (ZDR) now available for Enterprise via Frontier Safeguards