Claude Fable 5 and Claude Mythos 5

Today we're launching Claude Fable 5: a Mythos-class model that we've made safe for general use. Announcements Claude Fable 5 and Claude Mythos 5 Jun 9, 2026 Today we're launching Claude Fable 5 : a Mythos-class 1 model that we've made safe for general use. Fable 5's capabilities exceed those of any model we've ever made generally available.

It is state-of-the-art on nearly all tested benchmarks of AI capability, showing exceptional performance in software engineering, knowledge work, vision, scientific research, and many other areas. The longer and more complex the task, the larger Fable 5's lead over our other models. 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. We've therefore launched the model with safeguards that mean queries on some topics will instead receive a response from our next-most-capable model, Claude Opus 4.8. To release the model both safely and quickly, we've tuned these safeguards conservatively-they'll sometimes catch harmless requests, though they trigger, on average, in less than 5% of sessions.

With more capable models arriving in the coming months, we're working to improve our safeguards and reduce false positives as quickly as we can. For a small group of cyberdefenders and infrastructure providers, we're also launching Claude Mythos 5 . It's the same underlying model as Fable 5, but with the safeguards lifted in some areas.

2 Mythos 5 will initially be deployed through Project Glasswing , in collaboration with the US government, as an upgrade to Claude Mythos Preview. It has the strongest cybersecurity capabilities of any model in the world. Soon, we intend to expand access to Mythos 5 through a broader trusted access program.

The capabilities of models like Fable 5 and Mythos 5 have the potential to do profound good for the world. We've seen the beginnings of this in Project Glasswing, where the models have helped cyber defenders secure critically important software. We've also seen it in life sciences research, where the models are positing novel hypotheses and speeding up the development of new therapeutics.

Fable 5 and Mythos 5 are being offered at $10 per million input tokens and $50 per million output tokens-less than half the price of Claude Mythos Preview. Today's joint launch is another step towards our goal of bringing advanced AI capabilities to as many users as possible, as quickly and as safely as we can. Evaluating Claude Fable 5 and Claude Mythos 5 The table below compares the capabilities of Fable 5 and Mythos 5 to other leading models.

Fable 5 and Mythos 5 can work autonomously for longer than any previous Claude models. Below we discuss how these skills apply to software engineering, and cover the model's improved capabilities in knowledge work, vision, memory, and life sciences research. During early testing, Stripe reported that Fable 5 compressed months of engineering into days.

In a 50-million-line Ruby codebase, the model performed a codebase-wide migration in a day that would otherwise have taken a whole team over two months by hand. Fable 5 is also more token-efficient than past Claude models: on Cognition's FrontierCode evaluation, which tests whether models can pass difficult coding tasks while meeting the standards of high-quality production codebases, Fable 5 scores highest among frontier models, even at medium effort. Fable 5 shows strong performance on complex analytical tasks.

On Hebbia 's Finance Benchmark for senior-level reasoning, Fable 5 has the highest score of any model, with substantial gains in document-based reasoning, chart and table interpretation, and problem solving. IMC noted that Fable 5 aced their trading-analysis evaluations nearly across the board, including factual lookup, conceptual reasoning, root-cause analysis, and expected-value analysis.