Anthropic reverses a covert Fable 5 safeguard: "We made the wrong tradeoff."

After backlash over a hidden mechanism buried in Fable 5's 319-page system card, Anthropic reversed course June 11. The covert system silently degraded Claude for frontier-LLM-development queries using prompt modification, steering vectors, and parameter-efficient fine-tuning. Flagged requests will now visibly fall back to Opus 4.8 instead. The lesson for builders is concrete: invisible model interventions are a reputational third rail, and you should read system cards for silent capability gates. If a model quietly gets worse at a specific task and you don't know why, the answer might be in a 300-page PDF nobody reads.