diff --git a/codex-rs/core/config.schema.json b/codex-rs/core/config.schema.json
index bf2d97049..a2d974073 100644
--- a/codex-rs/core/config.schema.json
+++ b/codex-rs/core/config.schema.json
@@ -511,14 +511,6 @@
       },
       "type": "object"
     },
-    "ModeKind": {
-      "description": "Initial collaboration mode to use when the TUI starts.",
-      "enum": [
-        "plan",
-        "default"
-      ],
-      "type": "string"
-    },
     "ModelProviderInfo": {
       "additionalProperties": false,
       "description": "Serializable representation of a provider definition.",
@@ -1161,15 +1153,6 @@
           "description": "Enable animations (welcome screen, shimmer effects, spinners). Defaults to `true`.",
           "type": "boolean"
         },
-        "experimental_mode": {
-          "allOf": [
-            {
-              "$ref": "#/definitions/ModeKind"
-            }
-          ],
-          "default": null,
-          "description": "Start the TUI in the specified collaboration mode (plan/default). Defaults to unset."
-        },
         "notification_method": {
           "allOf": [
             {
diff --git a/codex-rs/core/src/config/mod.rs b/codex-rs/core/src/config/mod.rs
index c2b753f51..7b1e754df 100644
--- a/codex-rs/core/src/config/mod.rs
+++ b/codex-rs/core/src/config/mod.rs
@@ -57,7 +57,6 @@ use codex_app_server_protocol::Tools;
 use codex_app_server_protocol::UserSavedConfig;
 use codex_protocol::config_types::AltScreenMode;
 use codex_protocol::config_types::ForcedLoginMethod;
-use codex_protocol::config_types::ModeKind;
 use codex_protocol::config_types::Personality;
 use codex_protocol::config_types::ReasoningSummary;
 use codex_protocol::config_types::SandboxMode;
@@ -249,7 +248,6 @@ pub struct Config {
     pub show_tooltips: bool,
 
     /// Start the TUI in the specified collaboration mode (plan/default).
-    pub experimental_mode: Option<ModeKind>,
 
     /// Controls whether the TUI uses the terminal's alternate screen buffer.
     ///
@@ -1933,7 +1931,6 @@ impl Config {
                 .unwrap_or_default(),
             animations: cfg.tui.as_ref().map(|t| t.animations).unwrap_or(true),
             show_tooltips: cfg.tui.as_ref().map(|t| t.show_tooltips).unwrap_or(true),
-            experimental_mode: cfg.tui.as_ref().and_then(|t| t.experimental_mode),
             tui_alternate_screen: cfg
                 .tui
                 .as_ref()
@@ -2234,7 +2231,6 @@ phase_2_model = "gpt-5"
                 notification_method: NotificationMethod::Auto,
                 animations: true,
                 show_tooltips: true,
-                experimental_mode: None,
                 alternate_screen: AltScreenMode::Auto,
                 status_line: None,
             }
@@ -4237,7 +4233,6 @@ model_verbosity = "high"
                 tui_notification_method: Default::default(),
                 animations: true,
                 show_tooltips: true,
-                experimental_mode: None,
                 analytics_enabled: Some(true),
                 feedback_enabled: true,
                 tui_alternate_screen: AltScreenMode::Auto,
@@ -4351,7 +4346,6 @@ model_verbosity = "high"
             tui_notification_method: Default::default(),
             animations: true,
             show_tooltips: true,
-            experimental_mode: None,
             analytics_enabled: Some(true),
             feedback_enabled: true,
             tui_alternate_screen: AltScreenMode::Auto,
@@ -4463,7 +4457,6 @@ model_verbosity = "high"
             tui_notification_method: Default::default(),
             animations: true,
             show_tooltips: true,
-            experimental_mode: None,
             analytics_enabled: Some(false),
             feedback_enabled: true,
             tui_alternate_screen: AltScreenMode::Auto,
@@ -4561,7 +4554,6 @@ model_verbosity = "high"
             tui_notification_method: Default::default(),
             animations: true,
             show_tooltips: true,
-            experimental_mode: None,
             analytics_enabled: Some(true),
             feedback_enabled: true,
             tui_alternate_screen: AltScreenMode::Auto,
diff --git a/codex-rs/core/src/config/types.rs b/codex-rs/core/src/config/types.rs
index 80c16281b..36dd9924e 100644
--- a/codex-rs/core/src/config/types.rs
+++ b/codex-rs/core/src/config/types.rs
@@ -605,11 +605,6 @@ pub struct Tui {
     #[serde(default = "default_true")]
     pub show_tooltips: bool,
 
-    /// Start the TUI in the specified collaboration mode (plan/default).
-    /// Defaults to unset.
-    #[serde(default)]
-    pub experimental_mode: Option<ModeKind>,
-
     /// Controls whether the TUI uses the terminal's alternate screen buffer.
     ///
     /// - `auto` (default): Disable alternate screen in Zellij, enable elsewhere.
diff --git a/codex-rs/tui/src/chatwidget.rs b/codex-rs/tui/src/chatwidget.rs
index 0a6da6a5a..2201435ca 100644
--- a/codex-rs/tui/src/chatwidget.rs
+++ b/codex-rs/tui/src/chatwidget.rs
@@ -6210,10 +6210,7 @@ impl ChatWidget {
         if !config.features.enabled(Feature::CollaborationModes) {
             return None;
         }
-        let mut mask = match config.experimental_mode {
-            Some(kind) => collaboration_modes::mask_for_kind(models_manager, kind)?,
-            None => collaboration_modes::default_mask(models_manager)?,
-        };
+        let mut mask = collaboration_modes::default_mask(models_manager)?;
         if let Some(model_override) = model_override {
             mask.model = Some(model_override.to_string());
         }
diff --git a/codex-rs/tui/src/chatwidget/tests.rs b/codex-rs/tui/src/chatwidget/tests.rs
index 79232bddc..99cb96407 100644
--- a/codex-rs/tui/src/chatwidget/tests.rs
+++ b/codex-rs/tui/src/chatwidget/tests.rs
@@ -3739,7 +3739,7 @@ async fn collaboration_modes_defaults_to_code_on_startup() {
 }
 
 #[tokio::test]
-async fn experimental_mode_plan_applies_on_startup() {
+async fn experimental_mode_plan_is_ignored_on_startup() {
     let codex_home = tempdir().expect("tempdir");
     let cfg = ConfigBuilder::default()
         .codex_home(codex_home.path().to_path_buf())
@@ -3783,7 +3783,7 @@ async fn experimental_mode_plan_applies_on_startup() {
     };
 
     let chat = ChatWidget::new(init, thread_manager);
-    assert_eq!(chat.active_collaboration_mode_kind(), ModeKind::Plan);
+    assert_eq!(chat.active_collaboration_mode_kind(), ModeKind::Default);
     assert_eq!(chat.current_model(), resolved_model);
 }