Why Fable 5 Still Needs a Second Loop

Fable 5, Anthropic's latest AI model, released in June 2026, possesses the ability to autonomously verify its own code through self-written tests and vision, allowing it to handle complex tasks like writing code, running migrations, and validating outputs. This self-verification, while effective at understanding user intent and reasoning, operates as a probabilistic inner loop with inherent blind spots, necessitating an independent, deterministic outer loop to ensure structural soundness and prevent systematic faults. The AC/DC framework integrates Fable 5's self-verification within an independent verification stage, employing deterministic analysis to consistently enforce security, complexity, and conformance rules. This dual-loop system pairs the model's speed and intent with the certainty and traceability of independent checks, ensuring that autonomous operations are both efficient and reliable.