Claude Sonnet 5 Released by Anthropic: Fable and Mythos Services Restored

Anthropic has officially launched Claude Sonnet 5 and restored full access to its Fable and Mythos frontier models following completion of a comprehensive federal export control review.

The decision represents the conclusion of an eighteen-day operational pause that was triggered by a US government export control directive issued on June 12, which mandated the temporary suspension of Anthropic's highest-capability AI systems.

Government officials enacted the restriction after researchers at Amazon documented a method to bypass the safety controls of Fable 5, causing the model to identify software vulnerabilities and supply exploitation code.

Anthropic has since developed an updated automated classifier designed to patch the vulnerability, clearing the path for a full commercial rollout across its platform, cloud infrastructure, and partner networks.

The temporary suspension of Fable 5 and Mythos 5 highlighted the mounting regulatory pressures facing frontier intelligence systems. When the export control mandate took effect, the absence of real-time nationality verification systems necessitated a total access blackout for all global users.

🔍 Key Finding: Security evaluations conducted during the shutdown confirmed that the vulnerability identification behavior was not unique to Fable 5. Older and less capable architectures from multiple providers, including Claude Opus 4.8, GPT-5.5, and Kimi K2.7, replicated the exact results.

🛡️ Technical Resolution and Safety Measures

To resolve the federal directive, engineers trained an automated safety classifier targeting the specific bypass mechanism reported by Amazon. This software layer functions with a wide safety margin, identifying and blocking ambiguous developer prompts that display a statistical probability of malicious intent.

Internal validation data indicates the updated classifier prevents the reported exploitation technique in more than 99 percent of trials.

The expanded safety margin introduces a distinct trade-off for engineering teams, as the automated system flags benign requests more frequently during routine application development and software debugging.

🚀 Active Deployments and Agentic Workflows

While frontier models continue to face strict state oversight, the immediate commercial focus targets the newly-deployed Claude Sonnet 5, which is now available for enterprise and developer integration across multiple deployment environments.