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Frequently asked questions

Does using async def make every FastAPI endpoint faster?

No. Async routes help with concurrency when their I/O operations are awaitable; blocking database or HTTP calls can still stall the event loop. Review the complete call path, including dependencies and serialization. CPU-heavy tasks generally need a separate execution strategy, while load tests should measure latency, connection limits, and behavior under saturation.

Can a developer migrate FastAPI schemas to Pydantic v2?

Yes. The work can include replacing older validation patterns, reviewing model configuration, and updating serialization calls such as dict to model_dump. Check your FastAPI version and dependencies first. Contract tests should compare request validation, response payloads, and generated OpenAPI schemas, especially where clients depend on aliases, optional fields, or custom validators.

How should FastAPI manage SQLAlchemy async sessions?

Use a clear session lifecycle, commonly provided through a request-scoped dependency, and define transaction ownership explicitly. SQLAlchemy 2.0 AsyncSession should not be shared across concurrent tasks. Review connection-pool settings, cancellation behavior, and relationship loading, then test failure paths to confirm exceptions do not leave unfinished transactions or exhausted database connections.

Should long-running FastAPI jobs use BackgroundTasks or a queue?

FastAPI BackgroundTasks can suit small in-process follow-up operations, but it is not a durable job queue. Work requiring retries, scheduling, or recovery after process termination usually belongs in a separate worker system such as Celery. Model inference or document processing also needs decisions about job status, cancellation, duplicate submissions, and resource limits.

What testing skills should we look for in a FastAPI developer?

Look for experience with pytest, HTTPX, dependency overrides, and database-backed integration tests, not just mocked route tests. Ask how the engineer checks authentication failures, lifespan initialization, OpenAPI changes, and concurrent requests. A useful interview exercise is diagnosing an endpoint that passes functional tests but times out when a downstream service slows.

Are your developers really based in the US?

Yes. Every engineer lives and works in the United States. No offshore subcontracting and no hand-offs to another team. That's written into the contract.

How fast can someone start?

Most teams interview matched engineers within a week of the first call. Start dates depend on your interview process.