Serverless AI Inference Patterns: Cold Starts, Batching, and Cost Control at Scale

A fintech startup we worked with last quarter deployed a DistilBERT fraud-classification model on AWS Lambda behind API Gateway. Traffic looked fine in staging — 200 ms p50, 400 ms p99. Then production hit: the first Monday morning spike pushed p99 to 9.4 seconds, and three percent of requests timed out entirely. The model worked. The architecture didn't.