diff --git a/codex-rs/core/src/tools/handlers/multi_agents/spawn.rs b/codex-rs/core/src/tools/handlers/multi_agents/spawn.rs
index 67f109b738..5d4d1d6ac1 100644
--- a/codex-rs/core/src/tools/handlers/multi_agents/spawn.rs
+++ b/codex-rs/core/src/tools/handlers/multi_agents/spawn.rs
@@ -82,6 +82,9 @@ impl ToolHandler for Handler {
             .await;
         let mut config =
             build_agent_spawn_config(&session.get_base_instructions().await, turn.as_ref())?;
+        if let Some(service_tier) = args.service_tier.as_ref() {
+            config.service_tier = Some(service_tier.clone());
+        }
         if args.fork_context {
             reject_full_fork_spawn_overrides(
                 role_name,
diff --git a/codex-rs/core/src/tools/handlers/multi_agents_common.rs b/codex-rs/core/src/tools/handlers/multi_agents_common.rs
index 9c28b5426a..7058024acd 100644
--- a/codex-rs/core/src/tools/handlers/multi_agents_common.rs
+++ b/codex-rs/core/src/tools/handlers/multi_agents_common.rs
@@ -342,9 +342,13 @@ pub(crate) async fn apply_spawn_agent_service_tier(
     parent_service_tier: Option<&str>,
     requested_service_tier: Option<&str>,
 ) -> Result<(), FunctionCallError> {
-    let Some(candidate_service_tier) = requested_service_tier
-        .map(str::to_string)
-        .or_else(|| config.service_tier.clone())
+    let requested_service_tier_is_effective =
+        requested_service_tier.is_some_and(|requested_service_tier| {
+            config.service_tier.as_deref() == Some(requested_service_tier)
+        });
+    let Some(candidate_service_tier) = config
+        .service_tier
+        .clone()
         .or_else(|| parent_service_tier.map(str::to_string))
     else {
         config.service_tier = None;
@@ -366,7 +370,7 @@ pub(crate) async fn apply_spawn_agent_service_tier(
         return Ok(());
     }
 
-    if requested_service_tier.is_none() {
+    if !requested_service_tier_is_effective {
         config.service_tier = None;
         return Ok(());
     }
diff --git a/codex-rs/core/src/tools/handlers/multi_agents_tests.rs b/codex-rs/core/src/tools/handlers/multi_agents_tests.rs
index 94f8ed3d87..fa5dd442df 100644
--- a/codex-rs/core/src/tools/handlers/multi_agents_tests.rs
+++ b/codex-rs/core/src/tools/handlers/multi_agents_tests.rs
@@ -567,6 +567,52 @@ async fn spawn_agent_role_service_tier_persists_in_child_config() {
     );
 }
 
+#[tokio::test]
+async fn spawn_agent_role_service_tier_overrides_spawn_argument() {
+    #[derive(Debug, Deserialize)]
+    struct SpawnAgentResult {
+        agent_id: String,
+    }
+
+    let (mut session, mut turn) = make_session_and_context().await;
+    let role_name = install_role_with_service_tier(&mut turn, "gpt-5.4").await;
+    let manager = thread_manager();
+    let root = manager
+        .start_thread((*turn.config).clone())
+        .await
+        .expect("root thread should start");
+    session.services.agent_control = manager.agent_control();
+    session.conversation_id = root.thread_id;
+
+    let output = SpawnAgentHandler::default()
+        .handle(invocation(
+            Arc::new(session),
+            Arc::new(turn),
+            "spawn_agent",
+            function_payload(json!({
+                "message": "inspect this repo",
+                "agent_type": role_name,
+                "service_tier": "turbo"
+            })),
+        ))
+        .await
+        .expect("role-configured service tier should win over the spawn argument");
+    let (content, _) = expect_text_output(output);
+    let result: SpawnAgentResult =
+        serde_json::from_str(&content).expect("spawn_agent result should be json");
+    let snapshot = manager
+        .get_thread(parse_agent_id(&result.agent_id))
+        .await
+        .expect("spawned agent thread should exist")
+        .config_snapshot()
+        .await;
+
+    assert_eq!(
+        snapshot.service_tier,
+        Some(ServiceTier::Fast.request_value().to_string())
+    );
+}
+
 #[tokio::test]
 async fn spawn_agent_service_tier_override_rejects_unknown_tier() {
     let (session, turn) = make_session_and_context().await;
diff --git a/codex-rs/core/src/tools/handlers/multi_agents_v2/spawn.rs b/codex-rs/core/src/tools/handlers/multi_agents_v2/spawn.rs
index 79772be91f..5e4b7863a2 100644
--- a/codex-rs/core/src/tools/handlers/multi_agents_v2/spawn.rs
+++ b/codex-rs/core/src/tools/handlers/multi_agents_v2/spawn.rs
@@ -81,6 +81,9 @@ impl ToolHandler for Handler {
             .await;
         let mut config =
             build_agent_spawn_config(&session.get_base_instructions().await, turn.as_ref())?;
+        if let Some(service_tier) = args.service_tier.as_ref() {
+            config.service_tier = Some(service_tier.clone());
+        }
         if matches!(fork_mode, Some(SpawnAgentForkMode::FullHistory)) {
             reject_full_fork_spawn_overrides(
                 role_name,