Opus 5 answers ice cream question with a business plan

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.