Hamel Husain and Isaac Flath take Anthropic’s new anti-slop writing guidance and put it through an actual comparison: one question, three system prompts, and a verdict reached by reading the drafts out loud. (Seven-minute clip from their “Writing Evals With Isaac” live session.)
The thing being tested Anthropic published a named anti-pattern for its newest writing model, Claude Fable 5.1: mannered prose — metaphor and flourish substituted for direct statement The prompting guide treats it as a model-specific behavior. Fable 5.1’s writing is a step up from earlier Claude models (fewer stock phrases, less unexplained jargon), but in some cases it runs denser than Fable 5 — longer sentences, fewer paragraph breaks, more figurative phrasing standing in for plain statement The fix is one paragraph, pasted into a system prompt: Mannered prose substitutes metaphor and flourish for direct statement. Instead of “a parameter worth varying,” the mannered writer produces “a dial worth turning.” Instead of “this point still matters,” they write “this point earns its keep.” The phrases exist to display the writer, not to convey the idea, and readers can tell. That is why mannered prose irritates: it makes the reader work harder so the writer can perform. It is also imprecise. Metaphors drag in connotations the writer did not choose and cannot control. The fix is to say what you mean. When a literal phrase is available, use it.
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