diff --git a/codex-rs/core/src/codex.rs b/codex-rs/core/src/codex.rs
index 8a66fca0e..6401605ee 100644
--- a/codex-rs/core/src/codex.rs
+++ b/codex-rs/core/src/codex.rs
@@ -12,6 +12,7 @@ use crate::CodexAuth;
 use crate::SandboxState;
 use crate::agent::AgentControl;
 use crate::agent::AgentStatus;
+use crate::agent::MAX_THREAD_SPAWN_DEPTH;
 use crate::agent::agent_status_from_event;
 use crate::compact;
 use crate::compact::run_inline_auto_compact_task;
@@ -52,6 +53,7 @@ use codex_protocol::protocol::RawResponseItemEvent;
 use codex_protocol::protocol::ReviewRequest;
 use codex_protocol::protocol::RolloutItem;
 use codex_protocol::protocol::SessionSource;
+use codex_protocol::protocol::SubAgentSource;
 use codex_protocol::protocol::TurnAbortReason;
 use codex_protocol::protocol::TurnContextItem;
 use codex_protocol::protocol::TurnStartedEvent;
@@ -240,7 +242,7 @@ impl Codex {
     /// Spawn a new [`Codex`] and initialize the session.
     #[allow(clippy::too_many_arguments)]
     pub(crate) async fn spawn(
-        config: Config,
+        mut config: Config,
         auth_manager: Arc<AuthManager>,
         models_manager: Arc<ModelsManager>,
         skills_manager: Arc<SkillsManager>,
@@ -262,6 +264,12 @@ impl Codex {
             );
         }
 
+        if let SessionSource::SubAgent(SubAgentSource::ThreadSpawn { depth, .. }) = session_source
+            && depth >= MAX_THREAD_SPAWN_DEPTH
+        {
+            config.features.disable(Feature::Collab);
+        }
+
         let enabled_skills = loaded_skills.enabled_skills();
         let user_instructions = get_user_instructions(&config, Some(&enabled_skills)).await;
 
@@ -3587,6 +3595,7 @@ mod tests {
     use crate::shell::default_user_shell;
     use crate::tools::format_exec_output_str;
 
+    use codex_protocol::ThreadId;
     use codex_protocol::models::FunctionCallOutputPayload;
 
     use crate::protocol::CompactedItem;
diff --git a/codex-rs/core/src/tools/handlers/collab.rs b/codex-rs/core/src/tools/handlers/collab.rs
index 83ee53905..00190648f 100644
--- a/codex-rs/core/src/tools/handlers/collab.rs
+++ b/codex-rs/core/src/tools/handlers/collab.rs
@@ -1,8 +1,10 @@
 use crate::agent::AgentStatus;
+use crate::agent::exceeds_thread_spawn_depth_limit;
 use crate::codex::Session;
 use crate::codex::TurnContext;
 use crate::config::Config;
 use crate::error::CodexErr;
+use crate::features::Feature;
 use crate::function_tool::FunctionCallError;
 use crate::tools::context::ToolInvocation;
 use crate::tools::context::ToolOutput;
@@ -78,7 +80,7 @@ impl ToolHandler for CollabHandler {
 mod spawn {
     use super::*;
     use crate::agent::AgentRole;
-    use crate::agent::MAX_THREAD_SPAWN_DEPTH;
+
     use crate::agent::exceeds_thread_spawn_depth_limit;
     use crate::agent::next_thread_spawn_depth;
     use codex_protocol::protocol::SessionSource;
@@ -113,9 +115,9 @@ mod spawn {
         let session_source = turn.client.get_session_source();
         let child_depth = next_thread_spawn_depth(&session_source);
         if exceeds_thread_spawn_depth_limit(child_depth) {
-            return Err(FunctionCallError::RespondToModel(format!(
-                "agent depth limit reached: max depth is {MAX_THREAD_SPAWN_DEPTH}"
-            )));
+            return Err(FunctionCallError::RespondToModel(
+                "Agent depth limit reached. Solve the task yourself.".to_string(),
+            ));
         }
         session
             .send_event(
@@ -128,8 +130,11 @@ mod spawn {
                 .into(),
             )
             .await;
-        let mut config =
-            build_agent_spawn_config(&session.get_base_instructions().await, turn.as_ref())?;
+        let mut config = build_agent_spawn_config(
+            &session.get_base_instructions().await,
+            turn.as_ref(),
+            child_depth,
+        )?;
         agent_role
             .apply_to_config(&mut config)
             .map_err(FunctionCallError::RespondToModel)?;
@@ -582,6 +587,7 @@ fn collab_agent_error(agent_id: ThreadId, err: CodexErr) -> FunctionCallError {
 fn build_agent_spawn_config(
     base_instructions: &BaseInstructions,
     turn: &TurnContext,
+    child_depth: i32,
 ) -> Result<Config, FunctionCallError> {
     let base_config = turn.client.config();
     let mut config = (*base_config).clone();
@@ -607,6 +613,12 @@ fn build_agent_spawn_config(
         .map_err(|err| {
             FunctionCallError::RespondToModel(format!("sandbox_policy is invalid: {err}"))
         })?;
+
+    // If the new agent will be at max depth:
+    if exceeds_thread_spawn_depth_limit(child_depth + 1) {
+        config.features.disable(Feature::Collab);
+    }
+
     Ok(config)
 }
 
@@ -778,9 +790,9 @@ mod tests {
         };
         assert_eq!(
             err,
-            FunctionCallError::RespondToModel(format!(
-                "agent depth limit reached: max depth is {MAX_THREAD_SPAWN_DEPTH}"
-            ))
+            FunctionCallError::RespondToModel(
+                "Agent depth limit reached. Solve the task yourself.".to_string()
+            )
         );
     }
 
@@ -1144,7 +1156,7 @@ mod tests {
         turn.approval_policy = AskForApproval::Never;
         turn.sandbox_policy = SandboxPolicy::DangerFullAccess;
 
-        let config = build_agent_spawn_config(&base_instructions, &turn).expect("spawn config");
+        let config = build_agent_spawn_config(&base_instructions, &turn, 0).expect("spawn config");
         let mut expected = (*turn.client.config()).clone();
         expected.base_instructions = Some(base_instructions.text);
         expected.model = Some(turn.client.get_model());
@@ -1189,7 +1201,7 @@ mod tests {
             text: "base".to_string(),
         };
 
-        let config = build_agent_spawn_config(&base_instructions, &turn).expect("spawn config");
+        let config = build_agent_spawn_config(&base_instructions, &turn, 0).expect("spawn config");
 
         assert_eq!(config.user_instructions, base_config.user_instructions);
     }