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. But for a team where 90% of our codebase is Java 17+ Spring Boot services, the cracks showed fast: Context switching overhead: Java devs spent 15-20% of sprint time ramping up on Python async/await patterns, Pydantic validation, and Uvicorn deployment quirks — time that didn’t translate to our core Java stack.…