Anthropic has introduced Claude Fable 5, a new Mythos-class artificial intelligence model designed for general users while incorporating enhanced safety protections. The company describes it as the most capable Claude model currently available to the public.
According to Anthropic, Fable 5 delivers strong performance across a range of tasks, including software engineering, scientific research, visual analysis, knowledge work, memory-intensive applications, and long-running workflows.
The launch is particularly significant because Mythos-level AI systems were previously reserved for a limited group of cybersecurity experts and infrastructure providers through Project Glasswing.
Enhanced Safety Measures
Although Fable 5 is built on the same underlying architecture as Claude Mythos 5, Anthropic has added safeguards to make it suitable for broader use.
If users submit requests related to sensitive areas such as cybersecurity, biology and chemistry, or AI model distillation, the system automatically redirects those queries to Claude Opus 4.8. Users are informed whenever this fallback mechanism is activated.
Anthropic noted that these safeguards are intentionally conservative and may occasionally restrict harmless requests. However, the company estimates that fallback responses occur in fewer than 5 percent of user sessions.
Claude Mythos 5 Reserved for Approved Users
Alongside Fable 5, Anthropic has also launched Claude Mythos 5, a version intended for a smaller group of vetted users.
While both models share the same core technology, Mythos 5 operates with fewer restrictions in specific domains. Initially, access will be limited to Project Glasswing partners working in collaboration with the U.S. government.
The company plans to broaden access in the future through a trusted-access initiative aimed at cybersecurity organizations, as well as a separate program for selected researchers in the life sciences sector.
Strong Performance Across Industries
Anthropic claims that Fable 5 outperforms its previous public models on most major AI benchmarks.
In one example, fintech company Stripe reportedly used Fable 5 to complete a migration across a 50-million-line Ruby codebase in a single day. Anthropic stated that the same task would have taken a human team more than two months to complete manually.
The company also highlighted improvements in coding, financial reasoning, chart and table interpretation, scientific vision tasks, and handling long-context information.
Advancing Scientific Research
Anthropic says Mythos 5 has demonstrated promising capabilities in life sciences research.
According to the company, internal protein design teams used the model to accelerate parts of the drug discovery process by nearly ten times. In blinded evaluations, Anthropic researchers reportedly preferred Mythos 5’s molecular biology hypotheses over Opus-class outputs in approximately 80 percent of comparisons.
New Data Retention Policy
To address safety concerns, Anthropic is introducing a 30-day data retention policy for Fable 5, Mythos 5, and future models with similar capabilities.
The company emphasized that retained data will not be used to train future Claude models or for commercial purposes. Instead, the information will support efforts to identify jailbreak attempts, detect misuse, and reduce false-positive safety interventions.
Pricing and Availability
Claude Fable 5 is available immediately through the Claude API under the model name claude-fable-5.
Claude Mythos 5 will remain restricted to Project Glasswing partners until Anthropic expands access through its trusted-access program. Both models are priced at $10 per million input tokens and $50 per million output tokens.
Fable 5 is also accessible through consumption-based Enterprise plans. Users on Pro, Max, Team, and seat-based Enterprise subscriptions can use the model at no additional cost until June 22.
Beginning June 23, Fable 5 will no longer be included in those subscription plans, and users will need to purchase usage credits to continue accessing the model. Anthropic noted that the complimentary access period could be extended if capacity allows.
