Anthropic ships Claude Fable 5 and cyber-restricted Mythos 5, its most capable models

Anthropic positioned Fable 5 as a generational leap: built for long-running, autonomous agent work that can 'drive complex projects for days' without intervention, with the ability to understand diagrams, charts, and tables nested in documents and to proactively verify its own output. Pricing reported across sources ranged from $10/M input with $25–$50/M output, and the model carries a 1-million-token context window. Mythos 5 — the same underlying model with cyber safeguards removed — was described as the strongest cybersecurity model globally and limited to a vetted group.

Mechanically, Fable 5 routes flagged requests in cyber, biology, and chemistry domains to Claude Opus 4.8, a guardrail intended to prevent misuse while keeping the headline model broadly available. AWS's Swami Sivasubramanian and Matt Wood both posted that the launch brings 'Mythos-level capabilities to all customers' on Bedrock with the security, privacy, and data controls enterprises already run.

Competitively this raises the bar against GPT-5.5 and Gemini 3, especially on agentic coding: developer reaction (when safeguards didn't trigger) was 'close to unanimous and occasionally startled,' with reports of 10–20 point gains over Opus 4.8 on multi-file refactors and long agent runs. LlamaIndex's Jerry Liu cautioned the model is weak at document parsing — roughly equivalent to Gemini 3 Flash at 10–15x the token cost — and falls short of specialized OCR providers.

Benchmark opacity drew flak: Code Newsletter flagged that launch tables showed 'highest scores only' while ~21% of Terminal-Bench trials refused and fell back to Opus 4.8, creating an advertised-vs-actual gap. That refusal behavior and the safeguard routing set up the trust controversy that erupted within days.