A $500 RL fine-tune of a 9B open model beat frontier on catalog review at 68× lower cost per listing.

Fermisense reports a task-trained 9B open model reviewing e-commerce listings more accurately than the best frontier model they tested, for ~$500 total RL spend. The framing is scale economics: eBay carries ~2.5 billion live listings and Shopify absorbs 10M+ product updates daily, so per-listing cost dominates any accuracy edge. 225 points and 66 comments on HN. Caveat: the site returns 403 to direct fetching, so the figures come from indexed summary rather than a first-hand read of the methodology. (Fermisense)