Use the proxied url as the Jupyter server url

CHANGELOG.md

@@ -13,6 +13,7 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 ### Fixed
 - [#3916](https://github.com/plotly/dash/pull/3916) Fixed a regression where dragging multiple files into `dcc.Upload` would upload only the first file when `multiple=True`
 - [#3922](https://github.com/plotly/dash/pull/3922) Fix `dcc.Input(type="number")` stepper behavior when only `min` is set.
+- [#3925](https://github.com/plotly/dash/pull/3925) Use the proxied url as the Jupyter server url so `DASH_PROXY` is honored by the external url and inline iframe in notebooks.
 
 ## [4.4.1] - 2026-07-21
 

dash/dash.py

@@ -2605,6 +2605,14 @@ def verify_url_part(served_part, url_part, part_name):
                     extra_files.append(path)
 
         if jupyter_dash.active:
+            if jupyter_server_url is None and proxy:
+                # The app is served on host:port but reached through the proxy,
+                # so the notebook must display the proxied url.
+                proxied_url = urlparse(proxy.split("::")[1])
+                jupyter_server_url = (
+                    f"{proxied_url.scheme}://{proxied_url.hostname}"
+                    + (f":{proxied_url.port}" if proxied_url.port else "")
+                )
             jupyter_dash.run_app(
                 self,
                 mode=jupyter_mode,

tests/unit/test_configs.py

@@ -5,6 +5,7 @@
 from flask import Flask
 
 from dash import Dash, exceptions as _exc
+from dash._jupyter import jupyter_dash
 
 # noinspection PyProtectedMember
 from dash._configs import (
@@ -379,6 +380,21 @@ def test_proxy_success(mocker, caplog, empty_environ, proxy, host, port, path):
     assert "Dash is running on {}{}\n".format(proxy, path) in caplog.text
 
 
+def test_proxy_jupyter_server_url(mocker, empty_environ):
+    # The app is served on host:port but reached through the proxy, so the
+    # notebook must be given the proxied url.
+    proxy = "https://daash.plot.ly"
+    host, port = "127.0.0.1", 8050
+    app = Dash()
+    mocker.patch.object(app.server, "run")
+    mocker.patch.object(type(jupyter_dash), "active", True)
+    run_app = mocker.patch.object(jupyter_dash, "run_app")
+
+    app.run(proxy="http://{}:{}::{}".format(host, port, proxy), host=host, port=port)
+
+    assert run_app.call_args.kwargs["server_url"] == proxy
+
+
 def test_proxy_failure(mocker, empty_environ):
     app = Dash()