diff --git a/codex-rs/core/config.schema.json b/codex-rs/core/config.schema.json
index e70841c7d..e2d7b80b3 100644
--- a/codex-rs/core/config.schema.json
+++ b/codex-rs/core/config.schema.json
@@ -343,6 +343,16 @@
         }
       ]
     },
+    "ModeKind": {
+      "description": "Initial collaboration mode to use when the TUI starts.",
+      "enum": [
+        "plan",
+        "pair_programming",
+        "execute",
+        "custom"
+      ],
+      "type": "string"
+    },
     "ModelProviderInfo": {
       "additionalProperties": false,
       "description": "Serializable representation of a provider definition.",
@@ -953,6 +963,15 @@
           "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/execute/etc.). Defaults to unset."
+        },
         "notifications": {
           "allOf": [
             {
diff --git a/codex-rs/core/src/config/mod.rs b/codex-rs/core/src/config/mod.rs
index 4dde7e1ec..ca2f79edf 100644
--- a/codex-rs/core/src/config/mod.rs
+++ b/codex-rs/core/src/config/mod.rs
@@ -42,6 +42,7 @@ 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;
@@ -199,6 +200,9 @@ pub struct Config {
     /// Show startup tooltips in the TUI welcome screen.
     pub show_tooltips: bool,
 
+    /// Start the TUI in the specified collaboration mode (plan/execute/etc.).
+    pub experimental_mode: Option<ModeKind>,
+
     /// Controls whether the TUI uses the terminal's alternate screen buffer.
     ///
     /// This is the same `tui.alternate_screen` value from `config.toml` (see [`Tui`]).
@@ -1560,6 +1564,7 @@ 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()
@@ -1812,6 +1817,7 @@ persistence = "none"
                 notifications: Notifications::Enabled(true),
                 animations: true,
                 show_tooltips: true,
+                experimental_mode: None,
                 alternate_screen: AltScreenMode::Auto,
             }
         );
@@ -3697,6 +3703,7 @@ model_verbosity = "high"
                 tui_notifications: Default::default(),
                 animations: true,
                 show_tooltips: true,
+                experimental_mode: None,
                 analytics_enabled: Some(true),
                 feedback_enabled: true,
                 tui_alternate_screen: AltScreenMode::Auto,
@@ -3777,6 +3784,7 @@ model_verbosity = "high"
             tui_notifications: Default::default(),
             animations: true,
             show_tooltips: true,
+            experimental_mode: None,
             analytics_enabled: Some(true),
             feedback_enabled: true,
             tui_alternate_screen: AltScreenMode::Auto,
@@ -3872,6 +3880,7 @@ model_verbosity = "high"
             tui_notifications: Default::default(),
             animations: true,
             show_tooltips: true,
+            experimental_mode: None,
             analytics_enabled: Some(false),
             feedback_enabled: true,
             tui_alternate_screen: AltScreenMode::Auto,
@@ -3953,6 +3962,7 @@ model_verbosity = "high"
             tui_notifications: 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 350ae49a5..1b3f381d3 100644
--- a/codex-rs/core/src/config/types.rs
+++ b/codex-rs/core/src/config/types.rs
@@ -5,6 +5,7 @@
 
 use crate::config_loader::RequirementSource;
 pub use codex_protocol::config_types::AltScreenMode;
+pub use codex_protocol::config_types::ModeKind;
 pub use codex_protocol::config_types::Personality;
 pub use codex_protocol::config_types::WebSearchMode;
 use codex_utils_absolute_path::AbsolutePathBuf;
@@ -438,6 +439,11 @@ pub struct Tui {
     #[serde(default = "default_true")]
     pub show_tooltips: bool,
 
+    /// Start the TUI in the specified collaboration mode (plan/execute/etc.).
+    /// 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/protocol/src/config_types.rs b/codex-rs/protocol/src/config_types.rs
index c04479719..374a9d1b1 100644
--- a/codex-rs/protocol/src/config_types.rs
+++ b/codex-rs/protocol/src/config_types.rs
@@ -151,6 +151,16 @@ pub enum AltScreenMode {
     Never,
 }
 
+/// Initial collaboration mode to use when the TUI starts.
+#[derive(Clone, Copy, Debug, Serialize, Deserialize, PartialEq, Eq, Hash, JsonSchema, TS)]
+#[serde(rename_all = "snake_case")]
+pub enum ModeKind {
+    Plan,
+    PairProgramming,
+    Execute,
+    Custom,
+}
+
 /// Collaboration mode for a Codex session.
 #[derive(Clone, PartialEq, Eq, Hash, Debug, Serialize, Deserialize, JsonSchema, TS)]
 #[serde(tag = "mode", rename_all = "lowercase")]
diff --git a/codex-rs/tui/src/chatwidget.rs b/codex-rs/tui/src/chatwidget.rs
index ba894c3e9..bab19cc94 100644
--- a/codex-rs/tui/src/chatwidget.rs
+++ b/codex-rs/tui/src/chatwidget.rs
@@ -93,6 +93,7 @@ use codex_protocol::ThreadId;
 use codex_protocol::account::PlanType;
 use codex_protocol::approvals::ElicitationRequestEvent;
 use codex_protocol::config_types::CollaborationMode;
+use codex_protocol::config_types::ModeKind;
 use codex_protocol::config_types::Settings;
 use codex_protocol::models::local_image_label_text;
 use codex_protocol::parse_command::ParsedCommand;
@@ -1844,20 +1845,19 @@ impl ChatWidget {
         let codex_op_tx = spawn_agent(config.clone(), app_event_tx.clone(), thread_manager);
 
         let model_for_header = model.unwrap_or_else(|| DEFAULT_MODEL_DISPLAY_NAME.to_string());
+        let fallback_custom = Settings {
+            model: model_for_header.clone(),
+            reasoning_effort: None,
+            developer_instructions: None,
+        };
         let stored_collaboration_mode = if config.features.enabled(Feature::CollaborationModes) {
-            collaboration_modes::default_mode(models_manager.as_ref()).unwrap_or_else(|| {
-                CollaborationMode::Custom(Settings {
-                    model: model_for_header.clone(),
-                    reasoning_effort: None,
-                    developer_instructions: None,
-                })
-            })
+            initial_collaboration_mode(
+                models_manager.as_ref(),
+                fallback_custom,
+                config.experimental_mode,
+            )
         } else {
-            CollaborationMode::Custom(Settings {
-                model: model_for_header.clone(),
-                reasoning_effort: None,
-                developer_instructions: None,
-            })
+            CollaborationMode::Custom(fallback_custom)
         };
 
         let active_cell = Some(Self::placeholder_session_header_cell(
@@ -1969,20 +1969,19 @@ impl ChatWidget {
         let codex_op_tx =
             spawn_agent_from_existing(conversation, session_configured, app_event_tx.clone());
 
+        let fallback_custom = Settings {
+            model: header_model.clone(),
+            reasoning_effort: None,
+            developer_instructions: None,
+        };
         let stored_collaboration_mode = if config.features.enabled(Feature::CollaborationModes) {
-            collaboration_modes::default_mode(models_manager.as_ref()).unwrap_or_else(|| {
-                CollaborationMode::Custom(Settings {
-                    model: header_model.clone(),
-                    reasoning_effort: None,
-                    developer_instructions: None,
-                })
-            })
+            initial_collaboration_mode(
+                models_manager.as_ref(),
+                fallback_custom,
+                config.experimental_mode,
+            )
         } else {
-            CollaborationMode::Custom(Settings {
-                model: header_model.clone(),
-                reasoning_effort: None,
-                developer_instructions: None,
-            })
+            CollaborationMode::Custom(fallback_custom)
         };
 
         let mut widget = Self {
@@ -4296,9 +4295,13 @@ impl ChatWidget {
                 | CollaborationMode::Execute(settings)
                 | CollaborationMode::Custom(settings) => settings.clone(),
             };
+            let fallback_custom = settings.clone();
             self.stored_collaboration_mode = if enabled {
-                collaboration_modes::default_mode(self.models_manager.as_ref())
-                    .unwrap_or(CollaborationMode::Custom(settings))
+                initial_collaboration_mode(
+                    self.models_manager.as_ref(),
+                    fallback_custom,
+                    self.config.experimental_mode,
+                )
             } else {
                 CollaborationMode::Custom(settings)
             };
@@ -5031,6 +5034,24 @@ fn extract_first_bold(s: &str) -> Option<String> {
     None
 }
 
+fn initial_collaboration_mode(
+    models_manager: &ModelsManager,
+    fallback_custom: Settings,
+    desired_mode: Option<ModeKind>,
+) -> CollaborationMode {
+    if let Some(kind) = desired_mode {
+        if kind == ModeKind::Custom {
+            return CollaborationMode::Custom(fallback_custom);
+        }
+        if let Some(mode) = collaboration_modes::mode_for_kind(models_manager, kind) {
+            return mode;
+        }
+    }
+
+    collaboration_modes::default_mode(models_manager)
+        .unwrap_or(CollaborationMode::Custom(fallback_custom))
+}
+
 async fn fetch_rate_limits(base_url: String, auth: CodexAuth) -> Option<RateLimitSnapshot> {
     match BackendClient::from_auth(base_url, &auth) {
         Ok(client) => match client.get_rate_limits().await {
diff --git a/codex-rs/tui/src/collaboration_modes.rs b/codex-rs/tui/src/collaboration_modes.rs
index f48ad92c9..5497f373a 100644
--- a/codex-rs/tui/src/collaboration_modes.rs
+++ b/codex-rs/tui/src/collaboration_modes.rs
@@ -1,13 +1,6 @@
 use codex_core::models_manager::manager::ModelsManager;
 use codex_protocol::config_types::CollaborationMode;
-
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
-enum ModeKind {
-    Plan,
-    PairProgramming,
-    Execute,
-    Custom,
-}
+use codex_protocol::config_types::ModeKind;
 
 fn mode_kind(mode: &CollaborationMode) -> ModeKind {
     match mode {
@@ -27,6 +20,14 @@ pub(crate) fn default_mode(models_manager: &ModelsManager) -> Option<Collaborati
         .or_else(|| presets.into_iter().next())
 }
 
+pub(crate) fn mode_for_kind(
+    models_manager: &ModelsManager,
+    kind: ModeKind,
+) -> Option<CollaborationMode> {
+    let presets = models_manager.list_collaboration_modes();
+    presets.into_iter().find(|preset| mode_kind(preset) == kind)
+}
+
 pub(crate) fn same_variant(a: &CollaborationMode, b: &CollaborationMode) -> bool {
     mode_kind(a) == mode_kind(b)
 }