diff --git a/codex-rs/tui/src/app.rs b/codex-rs/tui/src/app.rs
index e47415d9f0..4273bc0686 100644
--- a/codex-rs/tui/src/app.rs
+++ b/codex-rs/tui/src/app.rs
@@ -1,8 +1,8 @@
 use crate::app_backtrack::BacktrackState;
 use crate::app_event::AppEvent;
 use crate::app_event::ExitMode;
-use crate::app_event::RealtimeAudioDeviceKind;
 use crate::app_event::ForkPanePlacement;
+use crate::app_event::RealtimeAudioDeviceKind;
 #[cfg(target_os = "windows")]
 use crate::app_event::WindowsSandboxEnableMode;
 use crate::app_event_sender::AppEventSender;
@@ -45,6 +45,7 @@ use codex_core::AuthManager;
 use codex_core::CodexAuth;
 use codex_core::CodexThread;
 use codex_core::ThreadManager;
+use codex_core::codex::SessionSettingsUpdate;
 use codex_core::config::Config;
 use codex_core::config::ConfigBuilder;
 use codex_core::config::ConfigOverrides;
@@ -98,6 +99,8 @@ use std::collections::BTreeMap;
 use std::collections::HashMap;
 use std::collections::HashSet;
 use std::collections::VecDeque;
+use std::fs;
+use std::io;
 use std::path::Path;
 use std::path::PathBuf;
 use std::sync::Arc;
@@ -115,6 +118,7 @@ use tokio::sync::mpsc::error::TrySendError;
 use tokio::sync::mpsc::unbounded_channel;
 use tokio::task::JoinHandle;
 use toml::Value as TomlValue;
+use uuid::Uuid;
 
 mod pending_interactive_replay;
 
@@ -1425,8 +1429,8 @@ impl App {
     }
 
     fn fresh_session_config(&self) -> Config {
-        let mut config = self.config.clone();
-        config.service_tier = self.chat_widget.current_service_tier();
+        let mut config = self.chat_widget.config_ref().clone();
+        config.model = Some(self.chat_widget.current_model().to_string());
         config
     }
 
@@ -1444,16 +1448,62 @@ impl App {
         let Some(multiplexer) = terminal_info.multiplexer.as_ref() else {
             return false;
         };
-        let description =
-            match spawn_fork_in_new_pane(multiplexer, &forked_thread_id, placement).await {
-                Ok(description) => description,
-                Err(err) => {
-                    self.chat_widget.add_error_message(format!(
-                        "Forked session created but failed to open a new pane: {err}"
-                    ));
-                    return false;
-                }
-            };
+        let thread_snapshot = forked_thread.config_snapshot().await;
+        let current_collaboration_mode = self.chat_widget.current_collaboration_mode();
+        let runtime_overrides = SessionSettingsUpdate {
+            cwd: Some(thread_snapshot.cwd.clone()),
+            approval_policy: Some(thread_snapshot.approval_policy),
+            sandbox_policy: Some(thread_snapshot.sandbox_policy.clone()),
+            windows_sandbox_level: None,
+            collaboration_mode: Some(CollaborationMode {
+                mode: self.chat_widget.active_collaboration_mode_kind(),
+                settings: Settings {
+                    model: thread_snapshot.model.clone(),
+                    reasoning_effort: thread_snapshot.reasoning_effort,
+                    developer_instructions: current_collaboration_mode
+                        .settings
+                        .developer_instructions
+                        .clone(),
+                },
+            }),
+            reasoning_summary: None,
+            service_tier: Some(self.chat_widget.current_service_tier()),
+            final_output_json_schema: None,
+            personality: thread_snapshot.personality,
+            app_server_client_name: None,
+        };
+        let runtime_overrides_path = match (|| -> io::Result<PathBuf> {
+            let overrides_dir = self.config.codex_home.join("tmp").join("runtime-overrides");
+            fs::create_dir_all(&overrides_dir)?;
+            let path = overrides_dir.join(format!("{}.json", Uuid::new_v4()));
+            let contents = serde_json::to_vec(&runtime_overrides).map_err(io::Error::other)?;
+            fs::write(&path, contents)?;
+            Ok(path)
+        })() {
+            Ok(path) => path,
+            Err(err) => {
+                self.chat_widget.add_error_message(format!(
+                    "Forked session created but failed to prepare runtime overrides: {err}"
+                ));
+                return false;
+            }
+        };
+        let description = match spawn_fork_in_new_pane(
+            multiplexer,
+            &forked_thread_id,
+            &runtime_overrides_path,
+            placement,
+        )
+        .await
+        {
+            Ok(description) => description,
+            Err(err) => {
+                self.chat_widget.add_error_message(format!(
+                    "Forked session created but failed to open a new pane: {err}"
+                ));
+                return false;
+            }
+        };
 
         self.suppressed_thread_created.insert(forked_thread_id);
         if let Err(err) = forked_thread.submit(Op::Shutdown).await {
@@ -5036,13 +5086,15 @@ mod tests {
     }
 
     #[tokio::test]
-    async fn fresh_session_config_uses_current_service_tier() {
+    async fn fresh_session_config_uses_live_chat_widget_state() {
         let mut app = make_test_app().await;
+        app.chat_widget.set_model("gpt-test");
         app.chat_widget
             .set_service_tier(Some(codex_protocol::config_types::ServiceTier::Fast));
 
         let config = app.fresh_session_config();
 
+        assert_eq!(config.model.as_deref(), Some("gpt-test"));
         assert_eq!(
             config.service_tier,
             Some(codex_protocol::config_types::ServiceTier::Fast)
diff --git a/codex-rs/tui/src/terminal_multiplexer.rs b/codex-rs/tui/src/terminal_multiplexer.rs
index 31ccd0bb7d..791e52b35d 100644
--- a/codex-rs/tui/src/terminal_multiplexer.rs
+++ b/codex-rs/tui/src/terminal_multiplexer.rs
@@ -3,6 +3,8 @@ use codex_core::terminal::Multiplexer;
 use codex_core::terminal::terminal_info;
 use codex_protocol::ThreadId;
 use shlex::try_join;
+use std::fs;
+use std::io;
 use std::path::Path;
 use std::path::PathBuf;
 use std::process::Command;
@@ -14,14 +16,42 @@ pub(crate) struct MultiplexerSpawnConfig {
 }
 
 fn codex_executable() -> PathBuf {
-    std::env::current_exe().unwrap_or_else(|_| PathBuf::from("codex"))
+    std::env::current_exe()
+        .map(|path| resolve_codex_executable(&path))
+        .unwrap_or_else(|_| PathBuf::from("codex"))
 }
 
-fn resume_command_parts(exe: &Path, thread_id: &ThreadId) -> Vec<String> {
+fn resolve_codex_executable(current_exe: &Path) -> PathBuf {
+    let Some(file_name) = current_exe.file_name().and_then(|name| name.to_str()) else {
+        return PathBuf::from("codex");
+    };
+    if !file_name.starts_with("codex-tui") {
+        return current_exe.to_path_buf();
+    }
+
+    let sibling = if let Some((_, extension)) = file_name.rsplit_once('.') {
+        current_exe.with_file_name(format!("codex.{extension}"))
+    } else {
+        current_exe.with_file_name("codex")
+    };
+    if sibling.is_file() {
+        sibling
+    } else {
+        PathBuf::from("codex")
+    }
+}
+
+fn resume_command_parts(
+    exe: &Path,
+    thread_id: &ThreadId,
+    runtime_overrides_path: &Path,
+) -> Vec<String> {
     vec![
         exe.display().to_string(),
         "resume".to_string(),
         thread_id.to_string(),
+        "--runtime-overrides".to_string(),
+        runtime_overrides_path.display().to_string(),
     ]
 }
 
@@ -86,9 +116,10 @@ fn fork_spawn_config(
     multiplexer: &Multiplexer,
     exe: &Path,
     thread_id: &ThreadId,
+    runtime_overrides_path: &Path,
     placement: Option<ForkPanePlacement>,
 ) -> MultiplexerSpawnConfig {
-    let resume_command = resume_command_parts(exe, thread_id);
+    let resume_command = resume_command_parts(exe, thread_id, runtime_overrides_path);
     match multiplexer {
         Multiplexer::Zellij {} => MultiplexerSpawnConfig {
             program: "zellij",
@@ -138,21 +169,97 @@ pub(crate) fn validate_fork_placement(placement: Option<ForkPanePlacement>) -> R
 pub(crate) async fn spawn_fork_in_new_pane(
     multiplexer: &Multiplexer,
     thread_id: &ThreadId,
+    runtime_overrides_path: &Path,
     placement: Option<ForkPanePlacement>,
 ) -> Result<&'static str, String> {
     let exe = codex_executable();
-    let config = fork_spawn_config(multiplexer, &exe, thread_id, placement);
+    let config = fork_spawn_config(
+        multiplexer,
+        &exe,
+        thread_id,
+        runtime_overrides_path,
+        placement,
+    );
     let MultiplexerSpawnConfig {
         program,
         args,
         description,
     } = config;
-    let status = tokio::task::spawn_blocking(move || Command::new(program).args(args).status())
-        .await
-        .map_err(|err| format!("failed to spawn {program} pane: {err}"))?;
+    let status = match tokio::task::spawn_blocking(move || {
+        Command::new(program).args(args).status()
+    })
+    .await
+    {
+        Ok(status) => status,
+        Err(err) => {
+            cleanup_runtime_overrides(runtime_overrides_path);
+            return Err(format!("failed to spawn {program} pane: {err}"));
+        }
+    };
     match status {
         Ok(status) if status.success() => Ok(description),
-        Ok(status) => Err(format!("{program} exited with status {status}")),
-        Err(err) => Err(format!("failed to run {program}: {err}")),
+        Ok(status) => {
+            cleanup_runtime_overrides(runtime_overrides_path);
+            Err(format!("{program} exited with status {status}"))
+        }
+        Err(err) => {
+            cleanup_runtime_overrides(runtime_overrides_path);
+            Err(format!("failed to run {program}: {err}"))
+        }
+    }
+}
+
+fn cleanup_runtime_overrides(path: &Path) {
+    if let Err(err) = fs::remove_file(path)
+        && err.kind() != io::ErrorKind::NotFound
+    {
+        tracing::warn!(path = %path.display(), error = %err, "failed to remove runtime overrides");
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use pretty_assertions::assert_eq;
+
+    #[test]
+    fn resolve_codex_executable_rewrites_codex_tui_to_sibling_codex() {
+        let tmp = tempfile::tempdir().expect("tempdir");
+        let current_exe = tmp.path().join("codex-tui");
+        let sibling_codex = tmp.path().join("codex");
+        std::fs::write(&sibling_codex, "").expect("write sibling codex");
+
+        let resolved = resolve_codex_executable(&current_exe);
+
+        assert_eq!(resolved, sibling_codex);
+    }
+
+    #[test]
+    fn resolve_codex_executable_keeps_non_tui_binary() {
+        let current_exe = PathBuf::from("/tmp/codex");
+
+        let resolved = resolve_codex_executable(&current_exe);
+
+        assert_eq!(resolved, current_exe);
+    }
+
+    #[test]
+    fn resume_command_parts_include_runtime_overrides() {
+        let exe = PathBuf::from("/tmp/codex");
+        let thread_id = ThreadId::new();
+        let runtime_overrides_path = PathBuf::from("/tmp/runtime-overrides.json");
+
+        let command = resume_command_parts(&exe, &thread_id, &runtime_overrides_path);
+
+        assert_eq!(
+            command,
+            vec![
+                "/tmp/codex".to_string(),
+                "resume".to_string(),
+                thread_id.to_string(),
+                "--runtime-overrides".to_string(),
+                "/tmp/runtime-overrides.json".to_string(),
+            ]
+        );
     }
 }