PART 1/3 OWNING INTELLIGENCE SERIES: HOW COINBASE BUILT, EVALUATED, AND POST-TRAINED A FRAUD AGENT

Summary from the TLDR Founders newsletter

Coinbase built an LLM risk agent onto Onramp's existing ML model and rules. Online A/B experiments showed a 30% reduction in fraudulent transactions and 22% less fraud value. Coinbase then post-trained Qwen3.5-9B on its proprietary Onramp fraud dataset. The resulting model outperformed Opus 4.5 on all fraud detection metrics while delivering 55% lower end-to-end online serving latency.