diff --git a/ragna/_ui/modal_configuration.py b/ragna/_ui/modal_configuration.py
index 7a62dd0a..a0c72fe2 100644
--- a/ragna/_ui/modal_configuration.py
+++ b/ragna/_ui/modal_configuration.py
@@ -49,13 +49,23 @@ class ChatConfig(param.Parameterized):
         bounds=(100, 10_000),
     )
 
+    def is_assistant_disabled(self):
+        return "Ragna/Demo" in self.assistant_name
+
+    def is_source_storage_disabled(self):
+        return "Ragna/Demo" in self.source_storage_name
+
     def to_params_dict(self):
-        return {
-            "chunk_overlap": self.chunk_overlap,
-            "chunk_size": self.chunk_size,
-            "num_tokens": self.max_context_tokens,
-            "max_new_tokens": self.max_new_tokens,
-        }
+        result = {}
+        if not self.is_assistant_disabled():
+            result["max_new_tokens"] = self.max_new_tokens
+
+        if not self.is_source_storage_disabled():
+            result["chunk_overlap"] = self.chunk_overlap
+            result["chunk_size"] = self.chunk_size
+            result["num_tokens"] = self.max_context_tokens
+
+        return result
 
 
 class ModalConfiguration(pn.viewable.Viewer):
@@ -65,6 +75,8 @@ class ModalConfiguration(pn.viewable.Viewer):
     new_chat_ready_callback = param.Callable()
     cancel_button_callback = param.Callable()
 
+    advanced_config_collapsed = param.Boolean(default=True)
+
     def __init__(self, api_wrapper, **params):
         super().__init__(chat_name=get_default_chat_name(), **params)
 
@@ -191,11 +203,14 @@ async def model_section(self):
             ),
         )
 
-    @pn.depends("config")
+    @pn.depends("config", "config.assistant_name", "config.source_storage_name")
     def advanced_config_ui(self):
         if self.config is None:
             return
 
+        disabled_assistant = self.config.is_assistant_disabled()
+        disabled_source_storage = self.config.is_source_storage_disabled()
+
         card = pn.Card(
             pn.Row(
                 pn.Column(
@@ -211,6 +226,8 @@ def advanced_config_ui(self):
                         bar_color=ui.MAIN_COLOR,
                         stylesheets=[ui.SS_LABEL_STYLE],
                         width_policy="max",
+                        disabled=disabled_source_storage,
+                        css_classes=["disabled"] if disabled_source_storage else [],
                     ),
                     pn.widgets.IntSlider.from_param(
                         self.config.param.chunk_overlap,
@@ -218,6 +235,8 @@ def advanced_config_ui(self):
                         bar_color=ui.MAIN_COLOR,
                         stylesheets=[ui.SS_LABEL_STYLE],
                         width_policy="max",
+                        disabled=disabled_source_storage,
+                        css_classes=["disabled"] if disabled_source_storage else [],
                     ),
                     margin=(0, 20, 0, 0),
                     width_policy="max",
@@ -234,12 +253,16 @@ def advanced_config_ui(self):
                         bar_color=ui.MAIN_COLOR,
                         stylesheets=[ui.SS_LABEL_STYLE],
                         width_policy="max",
+                        disabled=disabled_source_storage,
+                        css_classes=["disabled"] if disabled_source_storage else [],
                     ),
                     pn.widgets.IntSlider.from_param(
                         self.config.param.max_new_tokens,
                         bar_color=ui.MAIN_COLOR,
                         stylesheets=[ui.SS_LABEL_STYLE],
                         width_policy="max",
+                        disabled=disabled_assistant,
+                        css_classes=["disabled"] if disabled_assistant else [],
                     ),
                     width_policy="max",
                     height_policy="max",
@@ -250,14 +273,21 @@ def advanced_config_ui(self):
                 ),
                 height=250,
             ),
-            collapsed=True,
+            collapsed=self.advanced_config_collapsed,
             collapsible=True,
             hide_header=True,
             stylesheets=[ui.SS_ADVANCED_UI_CARD],
         )
 
         def toggle_card(event):
-            card.collapsed = not card.collapsed
+            if event.old < event.new:
+                # This callback is triggered when the card is rerendered,
+                # after changing the assistant, for example.
+                # This test prevents collapsing the card when it is not needed
+
+                card.collapsed = not card.collapsed
+                self.advanced_config_collapsed = card.collapsed
+
             toggle_button = event.obj
 
             if card.collapsed:
diff --git a/ragna/_ui/styles.py b/ragna/_ui/styles.py
index 847f5223..a3a73f7a 100644
--- a/ragna/_ui/styles.py
+++ b/ragna/_ui/styles.py
@@ -139,6 +139,22 @@ def divider():
 .noUi-handle, .noUi-connects {
     background-color: var(--clear-button-active);
 }
+
+.noUi-target[disabled='true'] {
+    border-color: darkgray;
+}
+
+
+.noUi-target[disabled='true'] .noUi-connect {
+    background-color: darkgray !important;
+}
+
+
+:host(.disabled) div.bk-slider-title {
+    color: darkgray !important;
+}
+
+
 """