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Public story · 2026-08-05 · high
The r/ClaudeAI post drew 411 upvotes as users confirmed system-prompt terseness instructions aren't optional with this model.
Why now: The thread had reached 411 upvotes on r/ClaudeAI by Aug. 5, the threshold that turned a prompting tip into something worth flagging.
Opus 5 turned an ice cream flavor question into a plan ending in a business loan and a storefront, per an r/ClaudeAI post with 411 upvotes. The thread confirms something that had mostly circulated as word of mouth: unless a system prompt tells Opus 5 to be concise, it defaults to full planning mode regardless of how small the ask is.
That default isn't a one-off glitch, per the same post: users say the model does this consistently unless a terseness instruction already sits in the system prompt. The ice cream example just happened to be small enough, and absurd enough, to make the pattern impossible to miss.
What the post actually changes is who knows about the fix. Terseness instructions for Opus 5 used to be something prompt engineers passed around on their own; a 411-upvote thread on r/ClaudeAI puts it in front of anyone new to the model who searches the subreddit.
The fix itself is one line in a system prompt. The bigger question the thread raises and doesn't answer is why Opus 5 ships defaulting to maximum scope in the first place.
Each link below shares sources, entities, or timing with this story.
Opus built by Anthropic / Shared entities / Same source domain / Earlier coverage
Linked by a graph relationship (Opus built by Anthropic); both cover ClaudeAI, Opus; reported by the same outlet (reddit.com).
Linked by a graph relationship (Opus built by Anthropic); both cover ClaudeAI, Opus; reported by the same outlet (reddit.com).
Opus built by Anthropic / Shared entity: Opus / Same source domain / Earlier coverage / Tension
Linked by a graph relationship (Opus built by Anthropic); both cover Opus; reported by the same outlet (reddit.com).
Opus built by Anthropic / Shared entity: Opus / Shared topic / Earlier coverage
Linked by a graph relationship (Opus built by Anthropic); both cover Opus; overlapping topics (ends, opus).
Linked by a graph relationship (Opus built by Anthropic); both cover Opus; overlapping topics (business, opus).
Opus built by Anthropic / Shared entity: ClaudeAI / Same source domain / Earlier coverage
Linked by a graph relationship (Opus built by Anthropic); both cover ClaudeAI; reported by the same outlet (reddit.com).
Linked by a graph relationship (Opus built by Anthropic); both cover ClaudeAI; reported by the same outlet (reddit.com).
Linked by a graph relationship (Opus built by Anthropic); both cover ClaudeAI; reported by the same outlet (reddit.com).