Anthropic has just introduced Claude Fable 5 and Claude Mythos 5, the most advanced artificial intelligence models the company has brought to the table to date.

From Anthropic they are quite direct about it. The company claims that Fable 5 outperforms any model they have made generally available to date, placing it at the state of the art in virtually every AI capability benchmark they have measured, including software engineering, knowledge work, computer vision, scientific research and much more. The promise is clear: the longer and more complex the task, the greater the advantage of Fable 5 over previous models from the same company.

What makes all of this especially interesting is that both Fable 5 and Mythos 5 share the same underlying model. The difference between the two is not in the engine, but in the safeguards. Claude Fable 5 is the secure version for general use, while Claude Mythos 5 is the same base but with certain restrictions lifted, initially intended for a small group of cyber defenders and critical infrastructure through Project Glasswing, an initiative in collaboration with the United States government.

Why Claude Fable 5 is a game changer

The first thing that stands out when reviewing the technical data is the level of performance that Anthropic has documented with real users. Stripe, for example, reported that Fable 5 compressed months of engineering into a matter of days. On a Ruby codebase of 50 million lines, the model completed a migration at scale in one day that would have required weeks of work for an entire team. That's not a marginal improvement, that's a paradigm shift.

In the financial field, the results are equally compelling. IMC confirmed that Fable 5 passed almost all of its trading analysis assessments, including fact finding, conceptual reasoning, and expected value analysis. Additionally, in Hebbia's finance benchmark for senior-level reasoning, Fable 5 scored the highest of any available model, with notable gains in document-based reasoning and graph interpretation.

The vision capabilities also deserve separate mention. The model can reconstruct the source code of a web application from screenshots and extract precise numbers from detailed scientific figures. For those who remember the limitations of previous versions, this represents a considerable leap.

Claude Mythos 5, the model reserved for the most critical

While Fable 5 is available to any user today, Mythos 5 operates on a different level. Anthropic describes it as having the most powerful cybersecurity capabilities of any AI system in the world. It is not a light comment. The company's own researchers subjected the model to tests where it demonstrated a remarkable ability to discover and exploit software vulnerabilities, surpassing even the capabilities of expert human operators.

That is why access to Mythos 5 is currently restricted. Project Glasswing, developed in direct collaboration with the US government, channels this model towards cyber defenders and critical infrastructure providers who need tools of this caliber. In life sciences research, Anthropic's in-house experts reported up to a tenfold speedup in aspects of the drug design process, with the model autonomously executing tasks normally completed by a scientist, from selecting binding sites to recovering from process failures.

Another striking fact is that Mythos 5 is the first Anthropic model to consistently produce novel and compelling scientific hypotheses. In blind comparisons against Opus-class models, company scientists preferred Mythos' molecular biology hypotheses in about 80% of cases, and several of those approaches have already advanced to experimental evaluation.

Availability and price: more accessible than expected

One of the most surprising details of the launch has to do with the price. Fable 5 and Mythos 5 are available for $10 per million input tokens and $50 per million output tokens, which is less than half the cost of Claude Mythos Preview. For developers who have been working with that model, it is very welcome news.

For users on subscription plans, Fable 5 is included at no additional cost on Pro, Max, Team, and Enterprise plans until June 22. After that date, its use will require consumer credits, although Anthropic has made clear that its intention is to reinstate it into standard subscription plans as soon as capacity allows.

In terms of safeguards, the model incorporates advanced security classifiers that detect potentially dangerous uses related to cybersecurity, biology, chemistry, and model distillation. When a query triggers those classifiers, the response is automatically generated by Claude Opus 4.8, a highly capable model in its own right. Anthropic notes that this occurs in less than 5% of sessions, so for the vast majority of users the performance is equivalent to that of pure Mythos 5.

The panorama that this launch describes is that of a company that has decided to no longer wait to bring its most powerful models to the general public, betting on a balance between security and accessibility that, until now, few in the industry had managed to articulate with such clarity.