Fable 5 blocks cancer researcher from every response, including "Hi"
A cancer researcher on the Max plan reports that Fable 5 refuses every single request — including greetings and weather questions — because its safety classifier reads their stored memory and preferences, which mention biology-related terms, before even looking at the message.
Score breakdown
Fable 5's context-aware classifier design means users with biology-related memory profiles are blocked from all responses regardless of message content, rendering the product entirely unusable for a segment of paying subscribers.
- 01u/SineCurve is a cancer researcher on Anthropic's Max plan whose Claude memory includes terms like prostate cancer, cell lines, immunofluorescence, and image analysis.
- 02Since Fable launched, every single request — including 'Hi,' R coding questions, weather, and World Cup queries — has been refused and fallen back to Opus 4.8.
- 03Fable's safety classifier reads stored memory, connectors, web results, and files before evaluating the user's latest message.
u/SineCurve, a self-described cancer researcher on Anthropic's Max plan, posted to r/ClaudeAI describing a complete inability to use Fable 5 since its launch. Every request — ranging from a simple "Hi" to R coding questions to asking about the weather or where to watch the World Cup — results in a refusal and a fallback to Opus 4.8. The researcher's stored Claude memory and preferences include terms like prostate cancer, cell lines, immunofluorescence, and image analysis, which they describe as "bread-and-butter academic stuff, nothing remotely weapon-adjacent."
The poster cites Anthropic's own support page as confirming this behavior, meaning a block can be triggered entirely by previously stored context rather than anything the user typed in the current session.
The root cause, as the poster explains it, is that Fable's safety classifier evaluates everything the model reads before it even processes the user's latest message — including memory, connectors, web results, and files. The poster cites Anthropic's own support page as confirming this behavior, meaning a block can be triggered entirely by previously stored context rather than anything the user typed in the current session. Incognito mode did not resolve the issue. The post highlights a sharp discrepancy between Anthropic's stated "under 5% of sessions" false positive rate — which the researcher argues must be an aggregate across all users — and the effective 100% block rate experienced by anyone whose profile contains biology-related terminology. The researcher concludes they are paying for a Max subscription and have never once successfully used Fable.
Key facts
- 01u/SineCurve is a cancer researcher on Anthropic's Max plan whose Claude memory includes terms like prostate cancer, cell lines, immunofluorescence, and image analysis.
- 02Since Fable launched, every single request — including 'Hi,' R coding questions, weather, and World Cup queries — has been refused and fallen back to Opus 4.8.
- 03Fable's safety classifier reads stored memory, connectors, web results, and files before evaluating the user's latest message.
- 04Anthropic's own support page confirms that blocks can be triggered by content the user did not type in the current session.
- 05Incognito mode did not resolve the issue.
- 06Anthropic's cited false positive rate is 'under 5% of sessions,' which the poster argues is an aggregate that masks a 100% block rate for users with biology-related profiles.
- 07The researcher states they are paying for Max and have never once successfully used Fable.
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