What is Mythos 5?

Mythos 5 is an AI model developed by Anthropic, referenced alongside Fable 5 in discussions about export controls and model capabilities.

• Jun 2026 - Nathaniel Whittemore said stopping models like Mythos 5 from being served to the public does nothing to slow development and may speed it up by freeing resources.
• Jul 2026 - Nathaniel Whittemore reported that the US government used an export control directive to demand Anthropic suspend Mythos 5 access for foreign nationals.
• Jul 2026 - Nathaniel Whittemore noted that Anthropic pointed out Opus is not trained on cyber tasks but still improved on finding vulnerabilities, similar to Mythos 5 in that aspect.