Yesterday, Anthropic introduced a Mythos-class model called Claude Fable 5, while for a small group of cyberdefenders and infrastructure providers, the company has also launched Claude Mythos 5.
Claude Fable 5 & Claude Mythos 5: Introduced
Claude Fable 5 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.
To avoid serious damage, the company has launched the model with safeguards that mean queries on some topics will instead receive a response from their next-most-capable model, Claude Opus 4.8.
Meanwhile, for a small group of cyberdefenders and infrastructure providers, Anthropic has also launched Claude Mythos 5. It’s the same underlying model as Fable 5, but with the safeguards lifted in some areas. Mythos 5 will initially be deployed through Project Glasswing, in collaboration with the US government, as an upgrade to Claude Mythos Preview. The company intends to expand access to Mythos 5 through a broader trusted access program.
Both models can work autonomously for longer than any previous Claude models in fields like Software Engineering, Knowledge work, Vision, Memory and long context, Drug design, novel hypotheses in molecular biology, novel research in genomics, and alignment.
The Fable 5 model comes with a new set of safety Classifiers: separate AI systems that detect potential misuse, including jailbreak attempts, and prevent the main model from responding. When Fable’s classifiers detect a request related to cybersecurity, biology, chemistry, or distillation, the response is automatically handled by Claude Opus 4.8 instead. Users will be informed whenever this occurs.
Anthropic has also announced a new data retention policy, where the company will require 30-day retention for all traffic on Mythos-class models, on both first and third-party surfaces.
Claude Mythos 5 and the Trusted Access Program
All users who currently have access to Claude Mythos Preview will be able to upgrade to Claude Mythos 5. In consultation with the US government, the company plans to steadily expand access to Claude Mythos 5.
The plans also include opening a trusted access program for biology. This program will provide access to Fable 5 with the biology and chemistry safeguards removed. It will enrol a small number of researchers from a variety of life science organisations spanning fundamental and translational research.
Availability
Claude Fable 5 is already available, while Claude Mythos 5 is restricted to Glasswing partners and will soon be available to select biology researchers only until the broader trusted access program is accessible.
Pricing for both models is $10 per million input tokens and $50 per million output tokens. Developers can use Claude Fable 5 via the Claude API.
On the Claude API and consumption-based Enterprise plans, Fable 5 is fully available. For subscription plans, the access will be rolled out more conservatively in stages:
- From June 9 through June 22, Fable 5 is included on Pro, Max, Team, and seat-based Enterprise plans at no extra cost.
- On June 23, Fable 5 will be removed from those plans. Using it after that will require usage credits. If capacity allows, the company will extend the included window.
- After this point—when sufficient capacity allows to do so—Anthropic aims to restore Fable 5 as a standard part of subscription plans.
