Dash 4.2: FastAPI and Quart Support

adamschroeder · June 12, 2026, 3:06pm

Plotly’s very own, Nathan Drezner, wrote about Dash 4.2 and the new FastAPI and Quart backend support within Dash.

Visit the the blog article to read all about it!

jinnyzor · June 12, 2026, 3:57pm

I’d also like to point out that you are not restricted to these as the only options as well.

This redesign grants you the flexibility to craft your own backend server and plug it in. It just need the same type of connections that the other backend servers have. Here is an example of a custom backend, it just currently extends a FastAPI server, but you can replace the shell server too

github.com/plotly/dash

tests/backend_tests/test_custom_backend.py

dev

import pytest
from dash import Dash, Input, Output, html, dcc
import traceback
import re

try:
    from dash.backends._fastapi import FastAPIDashServer
except ImportError:
    FastAPIDashServer = None


class CustomDashServer(FastAPIDashServer):
    def _get_traceback(self, _secret, error: Exception):
        tb = error.__traceback__
        errors = traceback.format_exception(type(error), error, tb)
        pass_errs = []
        callback_handled = False
        for err in errors:
            if self.error_handling_mode == "prune":
                if not callback_handled:

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This file contains the necessary definitions for the Dash workflow:

github.com/plotly/dash

dash/backends/base_server.py

dev

"""Base server abstractions for Dash backend implementations.

This module provides abstract base classes and protocols that define the interface
for different web server backends (Flask, Quart, FastAPI, etc.) to integrate with Dash.
"""
from __future__ import annotations

from abc import ABC, abstractmethod
from concurrent.futures import ThreadPoolExecutor
from typing import (
    Any,
    Dict,
    Type,
    TypeVar,
    Generic,
    Protocol,
    TYPE_CHECKING,
)

if TYPE_CHECKING:

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Dash 4.2: FastAPI and Quart Support

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