Streamlit to FastAPI Migration Guide 2026

When your Streamlit app outgrows its limits, migrating to FastAPI gives you full control, better performance, and production readiness. Here's how to do it right in 2026.

Why Migrate from Streamlit to FastAPI?

When Should You Migrate?

• You need custom login/logout, roles, or SSO
• You want a separate frontend (React, Vue, Svelte, HTMX)
• You have high concurrency or long-running tasks
• You need proper API documentation & client SDK generation
• Your app is moving to production with monitoring, scaling, etc.

Architecture Before vs After

Step-by-Step Migration Guide

1. Extract API logic
   Move data processing, database calls, and computations into FastAPI endpoints.

   
   # app/main.py
   from fastapi import FastAPI
   from pydantic import BaseModel
   
   app = FastAPI()
   
   class InputData(BaseModel):
       value: float
   
   @app.post("/calculate")
   async def calculate(data: InputData):
       result = data.value * 2  # your logic here
       return {"result": result}
                       

2. Replace Streamlit UI calls
   Use HTTP requests (fetch/axios) from frontend to call FastAPI.
3. Choose frontend
   Options in 2026:
   • HTMX + Jinja (simplest, no JS build step)
   • React/Vite (most powerful)
   • Vue/Nuxt (great for forms)
4. Migrate state
   Streamlit session_state → frontend localStorage/Redux or backend sessions (fastapi_sessions)
5. Deployment
   Dockerize FastAPI + frontend (or separate containers)

   
   FROM python:3.14-slim
   WORKDIR /app
   COPY requirements.txt .
   RUN pip install -r requirements.txt
   COPY . .
   CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000"]
                       

Common Gotchas & Tips

• Streamlit rerun → FastAPI stateless endpoints
• File uploads → use UploadFile in FastAPI
• Caching → Redis or in-memory with FastAPI Cache
• Auth → JWT/OAuth2 with FastAPI Users or Authlib
• Real-time → WebSockets in FastAPI