War Story: We Ditched FastAPI 0.109 for Spring Boot 3.3 and Cut API Latency by 30% for Java Teams

For our backend organization, 2024 started with a familiar tension: we’d adopted FastAPI 0.109 for new greenfield APIs to chase Python’s rapid prototyping speed, but our team of 22 Java developers was drowning in context switching. Six months post-adoption, we made the call to migrate all FastAPI workloads to Spring Boot 3.3 — and saw API p99 latency drop by 30% almost overnight.

The FastAPI Pain Points

FastAPI 0.109 delivered on its promise of quick setup: we had our first prototype live in 48 hours, with automatic OpenAPI docs and built-in request validation.…