Public Python API

The names exported from fastapi/__init__.py are the official public surface. Everything else under fastapi.* is documented but more likely to change.

from fastapi import ...

Name	Source module	Used for
FastAPI	fastapi.applications	The application class.
APIRouter	fastapi.routing	Sub-routing primitive.
Depends, Security	fastapi.param_functions	Dependency injection markers.
Body, Cookie, File, Form, Header, Path, Query	fastapi.param_functions	Parameter location markers.
Request, Response	fastapi.requests, fastapi.responses (re-exports of Starlette)	Direct request/response access.
WebSocket, WebSocketDisconnect	fastapi.websockets (re-export of Starlette)	WebSocket handling.
BackgroundTasks	fastapi.background	Per-request background work.
HTTPException, WebSocketException	fastapi.exceptions	Application-raised errors.
UploadFile	fastapi.datastructures	File uploads.
status	starlette.status (re-export)	HTTP status code constants.

These are the only names guaranteed stable across patch releases.

Sub-modules with stable API

Sub-module	Public items
fastapi.security	APIKeyQuery, APIKeyHeader, APIKeyCookie, HTTPBasic, HTTPBasicCredentials, HTTPBearer, HTTPDigest, HTTPAuthorizationCredentials, OAuth2, OAuth2PasswordBearer, OAuth2AuthorizationCodeBearer, OAuth2PasswordRequestForm, OAuth2PasswordRequestFormStrict, SecurityScopes, OpenIdConnect.
fastapi.encoders	jsonable_encoder.
fastapi.exceptions	The exception classes listed above plus RequestValidationError, WebSocketRequestValidationError, ResponseValidationError, FastAPIError.
fastapi.exception_handlers	The default async handlers (http_exception_handler, request_validation_exception_handler, websocket_request_validation_exception_handler).
fastapi.responses	Re-exports JSONResponse, HTMLResponse, PlainTextResponse, RedirectResponse, StreamingResponse, FileResponse, Response (all Starlette). Also exports EventSourceResponse from fastapi.sse and the deprecated UJSONResponse and ORJSONResponse.
fastapi.middleware.*	cors, gzip, httpsredirect, trustedhost, wsgi — re-exports of the Starlette middleware classes.
fastapi.staticfiles, fastapi.templating, fastapi.testclient	One-line re-exports of Starlette equivalents.
fastapi.openapi.docs	get_swagger_ui_html, get_redoc_html, get_swagger_ui_oauth2_redirect_html, swagger_ui_default_parameters.
fastapi.openapi.utils	get_openapi.
fastapi.openapi.models	The OpenAPI Pydantic models — useful for tools that build schemas.
fastapi.sse	EventSourceResponse, ServerSentEvent, format_sse_event.

Internal modules (likely to change)

These are used internally and not intended for direct import:

• fastapi._compat.* — Pydantic abstraction layer.
• fastapi.dependencies.* — Dependant and solve_dependencies. The names are public, but their signatures evolve to track Pydantic.
• fastapi.params — class versions of the parameter markers. User code should use the function wrappers from fastapi.param_functions (which is what from fastapi import Path resolves to).
• fastapi.utils — internal helpers (generate_unique_id, is_body_allowed_for_status_code, get_path_param_names, deep_dict_update).

Code that imports from these internal modules is allowed to break across patch releases.

Deprecated names still importable

Name	Replacement
fastapi.responses.UJSONResponse, ORJSONResponse	Set response_model and let Pydantic dump.
Param(..., regex=...)	Param(..., pattern=...).
fastapi.utils.generate_operation_id_for_path	fastapi.utils.generate_unique_id (called automatically).
on_startup= / on_shutdown=	lifespan= (an async context manager).

Each fires FastAPIDeprecationWarning at runtime. The classes/functions remain importable for backwards compatibility.