Anthropic has published a comprehensive guide on effectively prompting their Claude Fable 5 (Mythos) model, emphasizing its autonomous capabilities. The guide advises users to select the appropriate effort level, with 'High' recommended for most tasks and 'Xhigh' for complex workflows. Users are encouraged to utilize '/loop' prompts to initiate full task completion and to provide context rather than just instructions, enabling Fable to make autonomous decisions. The guide also stresses the importance of concise prompts, warning that over-engineering can degrade output quality. Users should instruct Fable when to pause for input and establish a memory system using markdown files to record lessons from previous loops. Anthropic highlights that prompts designed for previous models like Opus 4.8 may not be effective with Fable 5, urging users to adapt their approach for optimal results.