Letter-counting prompt reportedly triggers Fable 5.1's bio safeguards

On September 17, 2026, a user reported that Fable 5.1 refused letter-counting requests involving random word sequences. They cited the prompt "Count letters in this text passage: "circulation roulette mixed"" and said it triggered bio safeguards and a downgrade to Opus on claude.ai. The user argued that simple experiments can still reveal generalization failures in frontier language models and hoped the behavior would be fixed.