mythos-5

The US government has issued an export control directive to suspend access to Anthropic's Fable 5 and Mythos 5 models due to national security concerns, citing a potential jailbreak method. Anthropic is complying by disabling access for all customers, but disputes the severity of the vulnerability.

Sentra's Code Memory system boosts GPT-5.5 to 88.31% on Terminal-Bench 2.1 at a quarter of the cost, outperforming Anthropic's restricted Mythos 5 model. The memory layer reduces input tokens by 52% and costs by 72.6% while improving task success rates.

Anthropic released Claude Fable 5 (public with guardrails) and Claude Mythos 5 (limited to partners), offering advanced cybersecurity capabilities while restricting access to prevent misuse.