Coinbase took a free AI model, trained it on their own fraud data for a few weeks, and it now beats the most expensive model on the market at catching fraud. By a lot. Up to 35 points better on recall. The free model has 9 billion parameters. It runs on a single GPU. Here's why the big model never had a chance. Fraud patterns are proprietary. Coinbase's labeled fraud data has never touched the public internet, so no amount of pretraining compute buys you knowledge of it. Opus 4.5 walked into…