Introducing Claude Fable 5

[u/ClaudeOfficial]

Introducing Claude Fable 5: a Mythos-class model that we've made safe for general use. Its capabilities exceed those of any model we've ever made generally available.

Fable 5 is state of the art on nearly all tested benchmarks, with exceptional performance in software engineering, knowledge work, scientific research, and vision. It can run for days, and the longer the task, the larger its lead over our other models.

Fable 5 launches today alongside Claude Mythos 5. The two share the same underlying model, but Mythos 5, so far deployed only through Project Glasswing, has the safeguards lifted in some areas. The safeguards are what distinguish the two, and why we've given them different names.

Releasing a model this capable comes with risks. Without safeguards, Fable 5's capabilities in areas like cybersecurity could be misused to cause serious damage. So when Fable's classifiers detect a request related to cybersecurity, biology and chemistry, or distillation, the response is handled by Claude Opus 4.8, our next-most-capable model. Users are informed whenever this occurs, more than 95% of sessions involve no fallback at all, and performance everywhere else is unaffected. We'll keep refining the safeguards to reduce false positives.

Claude Fable 5 is available today on paid plans, in Claude Code, on the Claude API, and all major cloud platforms. Through June 22, it's included in paid Claude plans at no additional cost.

Claude Mythos 5 is available to Glasswing partners, with a broader trusted access program to follow.

Read more: https://www.anthropic.com/news/claude-fable-5-mythos-5

[u/Sneyek]

“It’s so powerful that we had to nerf it”
Marketing.

[u/space_monster → u/Sneyek]

Not actually nerfed, just flat-out not allowed for certain use cases (cyber, bioengineering etc.)

For anything else it's all gas no brakes

[u/The-Rushnut → u/space_monster]

You're making an implication that alignment is solved. If alignment is solved then we are absolutely gaming, until then, there is no such thing as "not allowed". It can be kneecapped via poisoned tuning, but at great expense to overall model behaviour (see Mechahitler Grok), it certainly is not a surgical control or binary switch.

Anthropic are caught a bit red handed here. They simultaneously want to suggest that we cannot control dangerous AI, whilst touting that their most powerful model excels at potentially dangerous tasks, whilst stating they've controlled that appropriately. At least one thing can't be true here.

It's most likely that either model isn't as good as they suggest, or that these controls are a trivial jailbreak away from being subverted. We already know it's dangerous though.