A Dial Worth Turning: Claude Opus 5's Prose, and the Style Guide Anthropic Wrote Against Its Own Model
Opus 5 writes 510 words where Opus 4.5 wrote 158, with 2.3 times the em dashes and twice the 'load-bearing'. Arena measured it, Hacker News named it, Reddit downgraded over it. Anthropic's answer arrived in Fable 5.1's prompting docs: a paragraph defining 'mannered prose', with the model's own tics as the examples, for you to paste into your prompt. The vendor wrote the style guide against its own model, and shipped it as your job.
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