diff --git a/codex-rs/code-mode-host/src/main.rs b/codex-rs/code-mode-host/src/main.rs
index 6b35d92021..b1e8735155 100644
--- a/codex-rs/code-mode-host/src/main.rs
+++ b/codex-rs/code-mode-host/src/main.rs
@@ -49,6 +49,7 @@ async fn run() -> Result<(), String> {
         sessions: Mutex::new(HashMap::new()),
         next_session_id: AtomicU64::new(1),
         peer,
+        host_id: std::process::id().to_string(),
     });
 
     let writer = tokio::spawn(async move {
@@ -110,8 +111,12 @@ impl HostState {
                 });
                 self.sessions.lock().await.insert(
                     session_id,
-                    Arc::new(CodeModeService::with_delegate(delegate)),
+                    Arc::new(CodeModeService::with_delegate_and_cell_id_prefix(
+                        delegate,
+                        self.host_id.clone(),
+                    )),
                 );
+    host_id: String,
                 self.respond(request_id, Ok(HostResponse::SessionCreated { session_id }))
                     .await;
             }
diff --git a/codex-rs/code-mode-host/tests/host.rs b/codex-rs/code-mode-host/tests/host.rs
index aa32957cd0..ce31eb8a96 100644
--- a/codex-rs/code-mode-host/tests/host.rs
+++ b/codex-rs/code-mode-host/tests/host.rs
@@ -25,6 +25,7 @@ async fn serves_code_mode_sessions_over_stdio() {
     .kill_on_drop(true)
     .spawn()
     .expect("spawn codex-code-mode-host");
+    let host_id = child.id().expect("host process id");
     let mut stdin = child.stdin.take().expect("host stdin");
     let mut stdout = child.stdout.take().expect("host stdout");
 
@@ -70,6 +71,7 @@ async fn serves_code_mode_sessions_over_stdio() {
         }) => cell_id,
         message => panic!("unexpected execute response: {message:?}"),
     };
+    assert_eq!(cell_id.as_str(), format!("{host_id}_1"));
     let response = match read_frame(&mut stdout)
         .await
         .expect("initial response frame")
diff --git a/codex-rs/code-mode/src/service.rs b/codex-rs/code-mode/src/service.rs
index ca53edbe54..d0856f484b 100644
--- a/codex-rs/code-mode/src/service.rs
+++ b/codex-rs/code-mode/src/service.rs
@@ -93,6 +93,7 @@ struct Inner {
     cells: Mutex<HashMap<CellId, CellHandle>>,
     delegate: Arc<dyn CodeModeSessionDelegate>,
     shutting_down: AtomicBool,
+    cell_id_prefix: Option<String>,
     next_cell_id: AtomicU64,
 }
 
@@ -106,24 +107,38 @@ impl CodeModeService {
     }
 
     pub fn with_delegate(delegate: Arc<dyn CodeModeSessionDelegate>) -> Self {
+        Self::with_inner(delegate, None)
+    }
+
+    pub fn with_delegate_and_cell_id_prefix(
+        delegate: Arc<dyn CodeModeSessionDelegate>,
+        cell_id_prefix: String,
+    ) -> Self {
+        Self::with_inner(delegate, Some(cell_id_prefix))
+    }
+
+    fn with_inner(
+        delegate: Arc<dyn CodeModeSessionDelegate>,
+        cell_id_prefix: Option<String>,
+    ) -> Self {
         Self {
             inner: Arc::new(Inner {
                 stored_values: Mutex::new(HashMap::new()),
                 cells: Mutex::new(HashMap::new()),
                 delegate,
                 shutting_down: AtomicBool::new(false),
+                cell_id_prefix,
                 next_cell_id: AtomicU64::new(1),
             }),
         }
     }
 
     fn allocate_cell_id(&self) -> CellId {
-        CellId::new(
-            self.inner
-                .next_cell_id
-                .fetch_add(1, Ordering::Relaxed)
-                .to_string(),
-        )
+        let cell_id = self.inner.next_cell_id.fetch_add(1, Ordering::Relaxed);
+        CellId::new(match &self.inner.cell_id_prefix {
+            Some(prefix) => format!("{prefix}_{cell_id}"),
+            None => cell_id.to_string(),
+        })
     }
 
     pub async fn execute(&self, request: ExecuteRequest) -> Result<StartedCell, String> {
@@ -823,6 +838,7 @@ mod tests {
         })
     }
 
+            cell_id_prefix: None,
     #[tokio::test]
     async fn synchronous_exit_returns_successfully() {
         let service = CodeModeService::new();
@@ -853,6 +869,27 @@ mod tests {
     async fn stored_values_are_shared_between_cells_but_not_sessions() {
         let first_session = CodeModeService::new();
         let second_session = CodeModeService::new();
+    #[tokio::test]
+    async fn cell_ids_include_the_configured_host_prefix() {
+        let service = CodeModeService::with_delegate_and_cell_id_prefix(
+            Arc::new(NoopCodeModeSessionDelegate),
+            "host7".to_string(),
+        );
+
+        let response = execute(&service, execute_request("text('done');")).await;
+
+        assert_eq!(
+            response,
+            RuntimeResponse::Result {
+                cell_id: cell_id("host7_1"),
+                content_items: vec![FunctionCallOutputContentItem::InputText {
+                    text: "done".to_string(),
+                }],
+                error_text: None,
+            }
+        );
+    }
+
 
         let write_response = execute(
             &first_session,