diff --git a/src/google/adk/cli/adk_web_server.py b/src/google/adk/cli/adk_web_server.py
index b073f1a7..f0cae1ae 100644
--- a/src/google/adk/cli/adk_web_server.py
+++ b/src/google/adk/cli/adk_web_server.py
@@ -436,6 +436,7 @@ class AdkWebServer:
       extra_plugins: Optional[list[str]] = None,
       logo_text: Optional[str] = None,
       logo_image_url: Optional[str] = None,
+      url_prefix: Optional[str] = None,
   ):
     self.agent_loader = agent_loader
     self.session_service = session_service
@@ -452,6 +453,7 @@ class AdkWebServer:
     self.runners_to_clean: set[str] = set()
     self.current_app_name_ref: SharedValue[str] = SharedValue(value="")
     self.runner_dict = {}
+    self.url_prefix = url_prefix
 
   async def get_runner_async(self, app_name: str) -> Runner:
     """Returns the cached runner for the given app."""
@@ -559,6 +561,7 @@ class AdkWebServer:
           " overwritten.",
           runtime_config_path,
       )
+    runtime_config["backendUrl"] = self.url_prefix if self.url_prefix else ""
 
     # Set custom logo config.
     if self.logo_text or self.logo_image_url:
@@ -1562,6 +1565,10 @@ class AdkWebServer:
       mimetypes.add_type("application/javascript", ".js", True)
       mimetypes.add_type("text/javascript", ".js", True)
 
+      redirect_dev_ui_url = (
+          self.url_prefix + "/dev-ui/" if self.url_prefix else "/dev-ui/"
+      )
+
       @app.get("/dev-ui/config")
       async def get_ui_config():
         return {
@@ -1571,11 +1578,11 @@ class AdkWebServer:
 
       @app.get("/")
       async def redirect_root_to_dev_ui():
-        return RedirectResponse("/dev-ui/")
+        return RedirectResponse(redirect_dev_ui_url)
 
       @app.get("/dev-ui")
       async def redirect_dev_ui_add_slash():
-        return RedirectResponse("/dev-ui/")
+        return RedirectResponse(redirect_dev_ui_url)
 
       app.mount(
           "/dev-ui/",
diff --git a/src/google/adk/cli/cli_tools_click.py b/src/google/adk/cli/cli_tools_click.py
index b841e017..009b96fe 100644
--- a/src/google/adk/cli/cli_tools_click.py
+++ b/src/google/adk/cli/cli_tools_click.py
@@ -1028,6 +1028,17 @@ def fast_api_common_options():
         ),
         multiple=True,
     )
+    @click.option(
+        "--url_prefix",
+        type=str,
+        help=(
+            "Optional. URL path prefix when the application is mounted behind a"
+            " reverse proxy or API gateway (e.g., '/api/v1', '/adk'). This"
+            " ensures generated URLs and redirects work correctly when the app"
+            " is not served at the root path. Must start with '/' if provided."
+        ),
+        default=None,
+    )
     @functools.wraps(func)
     @click.pass_context
     def wrapper(ctx, *args, **kwargs):
@@ -1065,6 +1076,7 @@ def cli_web(
     allow_origins: Optional[list[str]] = None,
     host: str = "127.0.0.1",
     port: int = 8000,
+    url_prefix: Optional[str] = None,
     trace_to_cloud: bool = False,
     otel_to_cloud: bool = False,
     reload: bool = True,
@@ -1128,6 +1140,7 @@ def cli_web(
       a2a=a2a,
       host=host,
       port=port,
+      url_prefix=url_prefix,
       reload_agents=reload_agents,
       extra_plugins=extra_plugins,
       logo_text=logo_text,
@@ -1164,6 +1177,7 @@ def cli_api_server(
     allow_origins: Optional[list[str]] = None,
     host: str = "127.0.0.1",
     port: int = 8000,
+    url_prefix: Optional[str] = None,
     trace_to_cloud: bool = False,
     otel_to_cloud: bool = False,
     reload: bool = True,
@@ -1203,6 +1217,7 @@ def cli_api_server(
           a2a=a2a,
           host=host,
           port=port,
+          url_prefix=url_prefix,
           reload_agents=reload_agents,
           extra_plugins=extra_plugins,
       ),
diff --git a/src/google/adk/cli/fast_api.py b/src/google/adk/cli/fast_api.py
index 7e1e18be..58dcfc15 100644
--- a/src/google/adk/cli/fast_api.py
+++ b/src/google/adk/cli/fast_api.py
@@ -64,6 +64,7 @@ def get_fast_api_app(
     a2a: bool = False,
     host: str = "127.0.0.1",
     port: int = 8000,
+    url_prefix: Optional[str] = None,
     trace_to_cloud: bool = False,
     otel_to_cloud: bool = False,
     reload_agents: bool = False,
@@ -144,6 +145,7 @@ def get_fast_api_app(
       extra_plugins=extra_plugins,
       logo_text=logo_text,
       logo_image_url=logo_image_url,
+      url_prefix=url_prefix,
   )
 
   # Callbacks & other optional args for when constructing the FastAPI instance