Anthropic Opens Access to Its Most Powerful AI Model Yet—But Not for Long

After months of speculation and careful deliberation, Anthropic has finally released the first publicly usable model from its new Mythos family: Claude Fable 5. The company had been testing the more powerful Claude Mythos Preview since April, but concerns about its ability to detect—and potentially exploit—cybersecurity vulnerabilities kept it under wraps. Now, Fable 5 arrives as a safer, more controlled alternative.

According to a detailed blog post, Fable 5 is Anthropic's most advanced AI model to date while still maintaining strong safety guardrails. It offers notable improvements in software engineering, knowledge work, and image understanding. In a quirky benchmark, the model even managed to beat Pokemon FireRed using only a vision-based AI interface—a feat previous models couldn't pull off.

But there's a catch: Fable 5 requires double the computing power of Anthropic's Opus models, so the company is rolling it out cautiously. Starting Tuesday, subscribers on Pro, Max, Team, and Enterprise plans can use Fable 5 until June 22. After that, the model disappears from the standard lineup, though users can still access it by burning usage credits—a pay-as-you-go system that may add extra fees if you exceed your allotment.

Safety was a major factor in the rollout. Anthropic says Fable 5 rejected every harmful single-turn request related to cyberattack planning, exploit development, and defense evasion, even when tested with 30 different jailbreak techniques. To prevent bioterror risks, Fable 5 won't answer most biology or chemistry questions; those are routed to Opus 4.8 instead. The company is also working with the U.S. government on future plans for the full Mythos 5 release.

For developers, Fable 5 is available now through the Claude API at $10 per million input tokens and $50 per million output tokens. Anthropic hasn't set a timeline for when—or if—Fable 5 will become a permanent part of its subscription plans.