How do you implement file uploads in FastAPI?

FastAPI handles file uploads with UploadFile and File: from fastapi import UploadFile, File; @app.post('/upload') async def upload(file: UploadFile = File(...)): contents = await file.read(); return {'name': file.filename, 'size': len(contents)}. For large files, avoid reading the entire file into memory — use file.file (SpooledTemporaryFile) and write in chunks or stream to cloud storage. Validate file type via file.content_type and extension. For multiple files: files: list[UploadFile] = File(...). Form data with files: mix UploadFile and Form fields in the same function signature. For production, upload directly to cloud storage (S3, GCS) rather than saving to local disk — use the aiobotocore or google-cloud-storage client in async context for streaming uploads without buffering the entire file.