We Moved Our API from Node to Bun. Here's What Broke (and What Got 3x Faster).

A 14-Second Build Dropped to 3 Seconds, Then Everything Else Went Wrong Six months ago, our API was a standard Express + TypeScript setup running on Node.js 22. It worked fine. Builds were slow, cold starts were sluggish, and our CI pipeline took 8 minutes, but it worked. Then our infra lead said the words every team dreads: "What if we just migrated to Bun?" Here's the full story -- the wins, the breakage, and the stuff nobody mentions in benchmark posts. Why We Pulled the Trigger Bun in 2026 is not the Bun of 2023. It's stable, it's battle-tested, and the numbers are hard to ignore. Cold startup time: Bun clocks in around 5ms versus Node's 50ms. For serverless functions and container restarts, that's a meaningful difference. Our API runs on Kubernetes with autoscaling, so cold starts directly impact p99 latency during traffic spikes. HTTP throughput: Bun's built-in HTTP server handles roughly 150,000 requests per second on simple JSON endpoints, compared to Node's 50,000. In practice