Anthropic launches Claude Fable 5 with Opus 4.8 fallback

Anthropic has launched Claude Fable 5, a public-facing model in its Mythos family designed to block outputs in specified high-risk categories and automatically fall back to Claude Opus 4.8 when queries are flagged. The company announced the model in a formal statement and said it will make Fable 5 available through the Claude API.

A separate Claude Mythos 5 will be distributed in a restricted preview. Users currently in the Mythos preview, including participants in Project Glasswing, can upgrade to Mythos 5 immediately. Anthropic said it plans to broaden access over time through a trusted-access program.

Fable 5 includes classifiers that prevent the model from performing tasks the company classifies as high risk. In such cases the system will defer to Opus 4.8 to provide an answer. Anthropic wrote that the fallback is intended to reduce the potential for misuse of the model’s capabilities.

Independent evaluations cited by Anthropic show performance gains. Analytics firm Hex reported Fable 5 scored above 90% on its core analytics benchmark and measured a ten-point improvement over Opus. Agentic workspace platform Genspark reported, “Fable came out #1 on our evals, winning head-to-head against every model we tested,” and noted stronger results on the hardest tasks, including user-interface design and game coding.

Anthropic described its safety testing as including more than 1,000 hours of internal bug-bounty work and engagement with outside red-teaming groups. The company wrote that those efforts did not produce a universal jailbreak for the model.

Pricing for Fable 5 is set at $10 per million input tokens and $50 per million output tokens. Developers can call the model through the Claude API. Mythos 5 access remains limited to Project Glasswing participants and other trusted-preview users.

Anthropic introduced the Mythos line earlier in a gated release to select industry partners. Fable 5 is the first wider public release from that line that uses automated guardrails to block certain high-risk outputs and rely on Opus 4.8 when needed.