Anthropic has launched its most powerful AI model, Claude Fable 5, to the general public for the first time, implementing safety guardrails. Fable 5 is the first publicly accessible version of the Mythos model, excelling in software engineering, knowledge work, and vision tasks, while imposing hard limits in high-risk areas like cybersecurity, biology, chemistry, and distillation, reverting to Claude Opus 4.8 when necessary. Initially limited to a handful of partners due to cybersecurity concerns, Anthropic expanded access to hundreds of organizations across 15 countries last week, now allowing anyone to access this technology through Anthropic's Claude API and consumption-based Enterprise plans.
The rollout of Fable 5 will be staged: by June 22, Fable 5 will be included in Pro, Max, Team, and seat-based Enterprise plans at no extra cost. After June 23, it will be removed from those plans, requiring usage credits, with plans to restore it as a standard subscription feature as soon as possible. Anthropic is also deploying a new version of Mythos, called Mythos 5, to organizations already approved for access to the advanced model.
The launch of Fable comes as Anthropic prepares to enter public markets, drawing attention alongside OpenAI and Elon Musk’s SpaceX. Anthropic warned that systems are advancing so rapidly that they may soon achieve recursive self-improvement (RSI), autonomously improving themselves without human intervention. To ensure safety, Anthropic stress-tested its classifiers with jailbreak attempts before releasing Fable 5, reporting no universal jailbreaks found in over 1,000 hours of testing.
However, novel attacks could still emerge. Consequently, with the launch of Fable 5 and Mythos 5, Anthropic will require a 30-day retention on all traffic, even if enterprises previously had zero-retention agreements. The company stated it will not use the data for training but only to “defend against complex and novel attacks, including new jailbreaks,” and “identify and reduce false positives.” This policy could set a precedent for mandatory data retention policies as a safety measure for accessing increasingly powerful models.
Not every query will receive a Fable 5 response, but Anthropic claims that cases requiring a fallback to Opus 4.8 are rare, with early data showing at least 95% of Fable sessions relying entirely on the model’s own responses. In third-party testing, analytics company Hex stated that Fable was the first to achieve a 90% on its core analytics benchmark for complex, long-running analytical tasks. Base44 noted that Fable excels at “one-shotting full apps” and has excellent tool-calling capabilities. Genspark claimed that Fable outperformed every other model in evaluations, significantly excelling in tasks like UI design and game coding.
Pricing for both Fable 5 and Mythos 5 is $10 per million input tokens and $50 per million output tokens, double the price of Opus 4.8, which may deter widespread usage. Many enterprises are becoming critical of AI costs after experiencing high bills or exhausting their annual budgets early. Anthropic anticipates high and unpredictable demand for Fable 5, with some, like shopping rewards platform Rakuten, believing the benefits outweigh the costs. “At the highest effort, Fable reflects on and validates its own work, making highly autonomous operations possible—the extra thinking pays for itself.”
Blogger's Review: The Claude Fable 5 by Anthropic strikes a delicate balance between safety and accessibility, and its 30-day data retention policy could lead to new industry standards. As AI technology evolves rapidly, the challenge will be how to foster innovation while ensuring safety. Enterprises must carefully evaluate the cost-benefit ratio, especially under tight budgets.