diff --git a/codex-rs/core/src/codex.rs b/codex-rs/core/src/codex.rs
index aa93404986..25b7b6cf36 100644
--- a/codex-rs/core/src/codex.rs
+++ b/codex-rs/core/src/codex.rs
@@ -6638,8 +6638,6 @@ mod tests {
     use codex_protocol::models::FunctionCallOutputBody;
     use codex_protocol::models::FunctionCallOutputPayload;
 
-    use crate::protocol::COLLABORATION_MODE_CLOSE_TAG;
-    use crate::protocol::COLLABORATION_MODE_OPEN_TAG;
     use crate::protocol::CompactedItem;
     use crate::protocol::CreditsSnapshot;
     use crate::protocol::InitialHistory;
@@ -8968,59 +8966,6 @@ mod tests {
         assert!(environment_update.contains("<timezone>Europe/Berlin</timezone>"));
     }
 
-    #[tokio::test]
-    async fn build_settings_update_items_emits_empty_collaboration_marker_when_instructions_clear()
-    {
-        let (session, previous_context) = make_session_and_context().await;
-        let previous_context = Arc::new(previous_context);
-        let mut current_context = previous_context
-            .with_model(
-                previous_context.model_info.slug.clone(),
-                &session.services.models_manager,
-            )
-            .await;
-        current_context.collaboration_mode = CollaborationMode {
-            mode: ModeKind::Default,
-            settings: Settings {
-                model: previous_context.collaboration_mode.model().to_string(),
-                reasoning_effort: previous_context.collaboration_mode.reasoning_effort(),
-                developer_instructions: None,
-            },
-        };
-
-        let mut previous_context_item = previous_context.to_turn_context_item();
-        previous_context_item.collaboration_mode = Some(CollaborationMode {
-            mode: ModeKind::Realtime,
-            settings: Settings {
-                model: previous_context.collaboration_mode.model().to_string(),
-                reasoning_effort: previous_context.collaboration_mode.reasoning_effort(),
-                developer_instructions: Some("realtime instructions".to_string()),
-            },
-        });
-
-        let update_items = session.build_settings_update_items(
-            Some(&previous_context_item),
-            None,
-            &current_context,
-        );
-
-        let developer_update = update_items
-            .iter()
-            .find_map(|item| match item {
-                ResponseItem::Message { role, content, .. } if role == "developer" => {
-                    let [ContentItem::InputText { text }] = content.as_slice() else {
-                        return None;
-                    };
-                    Some(text)
-                }
-                _ => None,
-            })
-            .expect("developer update item should be emitted");
-        assert!(developer_update.contains(&format!(
-            "{COLLABORATION_MODE_OPEN_TAG}{COLLABORATION_MODE_CLOSE_TAG}"
-        )));
-    }
-
     #[tokio::test]
     async fn shutdown_resets_realtime_collaboration_mode_to_default() {
         let (session, _turn_context, _rx) = make_session_and_context_with_rx().await;
diff --git a/codex-rs/core/src/context_manager/updates.rs b/codex-rs/core/src/context_manager/updates.rs
index 5d138ecc62..80fae0c988 100644
--- a/codex-rs/core/src/context_manager/updates.rs
+++ b/codex-rs/core/src/context_manager/updates.rs
@@ -8,8 +8,6 @@ use codex_protocol::models::ContentItem;
 use codex_protocol::models::DeveloperInstructions;
 use codex_protocol::models::ResponseItem;
 use codex_protocol::openai_models::ModelInfo;
-use codex_protocol::protocol::COLLABORATION_MODE_CLOSE_TAG;
-use codex_protocol::protocol::COLLABORATION_MODE_OPEN_TAG;
 use codex_protocol::protocol::TurnContextItem;
 
 fn build_environment_update_item(
@@ -56,21 +54,12 @@ fn build_collaboration_mode_update_item(
 ) -> Option<DeveloperInstructions> {
     let prev = previous?;
     if prev.collaboration_mode.as_ref() != Some(&next.collaboration_mode) {
-        Some(
-            DeveloperInstructions::from_collaboration_mode(&next.collaboration_mode)
-                .unwrap_or_else(empty_collaboration_mode_update),
-        )
+        DeveloperInstructions::from_collaboration_mode(&next.collaboration_mode)
     } else {
         None
     }
 }
 
-fn empty_collaboration_mode_update() -> DeveloperInstructions {
-    DeveloperInstructions::new(format!(
-        "{COLLABORATION_MODE_OPEN_TAG}{COLLABORATION_MODE_CLOSE_TAG}"
-    ))
-}
-
 fn build_personality_update_item(
     previous: Option<&TurnContextItem>,
     next: &TurnContext,
diff --git a/codex-rs/core/tests/suite/collaboration_instructions.rs b/codex-rs/core/tests/suite/collaboration_instructions.rs
index 3134cef85b..7d799dc19f 100644
--- a/codex-rs/core/tests/suite/collaboration_instructions.rs
+++ b/codex-rs/core/tests/suite/collaboration_instructions.rs
@@ -622,7 +622,6 @@ async fn collaboration_mode_update_emits_empty_marker_when_instructions_clear()
     let input = req2.single_request().input();
     let dev_texts = developer_texts(&input);
     assert_eq!(count_exact(&dev_texts, &collab_xml(realtime_text)), 1);
-    assert_eq!(count_exact(&dev_texts, &collab_xml("")), 1);
 
     Ok(())
 }
@@ -783,58 +782,3 @@ async fn resume_replays_collaboration_instructions() -> Result<()> {
 
     Ok(())
 }
-
-#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-async fn empty_collaboration_instructions_emit_empty_marker() -> Result<()> {
-    skip_if_no_network!(Ok(()));
-
-    let server = start_mock_server().await;
-    let req = mount_sse_once(
-        &server,
-        sse(vec![ev_response_created("resp-1"), ev_completed("resp-1")]),
-    )
-    .await;
-
-    let test = test_codex().build(&server).await?;
-    let current_model = test.session_configured.model.clone();
-
-    test.codex
-        .submit(Op::OverrideTurnContext {
-            cwd: None,
-            approval_policy: None,
-            sandbox_policy: None,
-            windows_sandbox_level: None,
-            model: None,
-            effort: None,
-            summary: None,
-            collaboration_mode: Some(CollaborationMode {
-                mode: ModeKind::Default,
-                settings: Settings {
-                    model: current_model,
-                    reasoning_effort: None,
-                    developer_instructions: Some("".to_string()),
-                },
-            }),
-            personality: None,
-        })
-        .await?;
-
-    test.codex
-        .submit(Op::UserInput {
-            items: vec![UserInput::Text {
-                text: "hello".into(),
-                text_elements: Vec::new(),
-            }],
-            final_output_json_schema: None,
-        })
-        .await?;
-    wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
-
-    let input = req.single_request().input();
-    let dev_texts = developer_texts(&input);
-    assert_eq!(dev_texts.len(), 2);
-    let collab_text = collab_xml("");
-    assert_eq!(count_exact(&dev_texts, &collab_text), 1);
-
-    Ok(())
-}