Statement on the US government directive to suspend access to Fable 5 and Mythos 5

The US government issued an export control directive to suspend access to Anthropic's Fable 5 and Mythos 5 models, citing national security concerns over a potential jailbreak method. Anthropic complied by abruptly disabling the models for all customers, though it disputes the uniqueness of the vulnerability, noting other publicly-available models can achieve similar results.

Statement on the US government directive to suspend access to Fable 5 and Mythos 5 https://www.anthropic.com/news/fable-mythos-access The US government, citing national security authorities, has issued an export control directive to suspend all access to Fable 5 and Mythos 5 by any foreign national, whether inside or outside the United States, including foreign national Anthropic employees. The net effect of this order is that we must abruptly disable Fable 5 and Mythos 5 for allour customers to ensure compliance.Access to all other Anthropic modelswill not be affected.We received the directive from the government today at 5:21pm ET . The letter did not provide specific details of its national security concern. Our understanding is that the government believes it has become aware of a method of bypassing, or "jailbreaking" Fable 5. We reviewed a demonstration of this specific technique being used to identify a small number of previously known, minor vulnerabilities. These vulnerabilities all appear relatively simple, and we have found that other publicly-available models are able to discover them as well without requiring a bypass. ... To date, the government has only given us verbal evidence of a potential narrow, non-universal jailbreak, which essentially consists of asking the model to read a specific codebase and fix any software flaws. Our understanding is that one potential jailbreak was shared with the government. We have reviewed the report and validated that the level of capability displayed there is widely available from other models including OpenAI's GPT-5.5 , and is used every day by the defenders who keep systems safe. We will share more details over the next 24 hours. I still have access to Fable via claude.ai https://claude.ai/ and Claude Code now, at 9:01pm ET. Update : I ran this script https://gist.github.com/simonw/5894cfafc64a2b8aafbe834bc9c950b9 against the Anthropic API to spot when claude-fable-5 would stop working. My access was cut off at 6:59pm Pacific 9:59pm ET : 2026-06-12T18:56:50-07:00 attempt 35: running uv run llm -m claude-fable-5 hi 2026-06-12T18:56:55-07:00 success: Hi there How can I help you today? 2026-06-12T18:57:55-07:00 attempt 36: running uv run llm -m claude-fable-5 hi 2026-06-12T18:57:59-07:00 success: Hi How can I help you today? 2026-06-12T18:58:59-07:00 attempt 37: running uv run llm -m claude-fable-5 hi 2026-06-12T18:59:00-07:00 FAILED after attempt 37 with exit code 1 stderr: Error: Error code: 404 - {'type': 'error', 'error': {'type': 'not found error', 'message': 'Claude Fable 5 is not available. Please use Opus 4.8. Learn more: https://www.anthropic.com/news/fable-mythos-access'}, 'request id': 'req 011CbzRyirV7KZLHYYdBM9od'} Via @AnthropicAI https://twitter.com/AnthropicAI/status/2065597531644743999 Tags: jailbreaking https://simonwillison.net/tags/jailbreaking , ai https://simonwillison.net/tags/ai , generative-ai https://simonwillison.net/tags/generative-ai , llms https://simonwillison.net/tags/llms , anthropic https://simonwillison.net/tags/anthropic , claude https://simonwillison.net/tags/claude , ai-ethics https://simonwillison.net/tags/ai-ethics , claude-mythos https://simonwillison.net/tags/claude-mythos