diff --git a/products/tasks/backend/presentation/serializers.py b/products/tasks/backend/presentation/serializers.py
index 398351a454b3..6783ae197d05 100644
--- a/products/tasks/backend/presentation/serializers.py
+++ b/products/tasks/backend/presentation/serializers.py
@@ -2041,7 +2041,12 @@ class TaskRunBootstrapCreateRequestSerializer(
     PR_AUTHORSHIP_MODE_CHOICES = [mode.value for mode in PrAuthorshipMode]
     RUN_SOURCE_CHOICES = [source.value for source in RunSource]
     RUNTIME_ADAPTER_CHOICES = [adapter.value for adapter in RuntimeAdapter]
-    REASONING_EFFORT_CHOICES = [effort.value for effort in PUBLIC_REASONING_EFFORTS]
+    PI_THINKING_LEVEL_CHOICES = ("off", "minimal", "low", "medium", "high", "xhigh", "max")
+    REASONING_EFFORT_CHOICES = [
+        "off",
+        "minimal",
+        *(effort.value for effort in PUBLIC_REASONING_EFFORTS),
+    ]
 
     environment = serializers.ChoiceField(
         choices=[environment.value for environment in tasks_facade.TaskRunEnvironment],
@@ -2163,6 +2168,37 @@ def validate(self, attrs):
             errors["relayed_mcp_servers"] = collision_error
         initial_permission_mode = attrs.get("initial_permission_mode")
         runtime_adapter = attrs.get("runtime_adapter")
+        view = self.context.get("view")
+        request = self.context.get("request")
+        task_id = view._task_id() if view else None
+        is_pi_task = (
+            task_id is not None
+            and request is not None
+            and tasks_facade.task_runtime(
+                task_id,
+                self.context["team"].id,
+                request.user.id,
+                for_control=True,
+            )
+            == tasks_facade.TaskRuntime.PI
+        )
+        if is_pi_task:
+            if runtime_adapter is not None:
+                errors["runtime_adapter"] = "This field cannot be used with a Pi task."
+            if attrs.get("context_window") is not None:
+                errors["context_window"] = "This field cannot be used with a Pi task."
+            if attrs.get("fast_mode") is not None:
+                errors["fast_mode"] = "This field cannot be used with a Pi task."
+            if initial_permission_mode is not None:
+                errors["initial_permission_mode"] = "This field cannot be used with a Pi task."
+            if (
+                attrs.get("reasoning_effort") is not None
+                and attrs["reasoning_effort"] not in self.PI_THINKING_LEVEL_CHOICES
+            ):
+                errors["reasoning_effort"] = "This thinking level is not supported by Pi."
+            if errors:
+                raise serializers.ValidationError(errors)
+            return attrs
         if initial_permission_mode is not None:
             if runtime_adapter is None:
                 errors["initial_permission_mode"] = "This field requires runtime_adapter to be set."
diff --git a/products/tasks/backend/tests/test_api.py b/products/tasks/backend/tests/test_api.py
index ece88a369fcd..f2c100e56b50 100644
--- a/products/tasks/backend/tests/test_api.py
+++ b/products/tasks/backend/tests/test_api.py
@@ -2206,6 +2206,43 @@ def test_create_run_endpoint_creates_cloud_run_without_triggering_workflow(self,
         self.assertEqual(task_run.state["auto_publish"], True)
         mock_workflow.assert_not_called()
 
+    def test_create_run_endpoint_uses_pi_model_without_an_acp_adapter(self):
+        task = self.create_task(runtime=Task.Runtime.PI)
+
+        response = self.client.post(
+            f"/api/projects/@current/tasks/{task.id}/runs/",
+            {
+                "environment": "cloud",
+                "mode": "interactive",
+                "model": "gpt-5.6-terra",
+                "reasoning_effort": "high",
+            },
+            format="json",
+        )
+
+        self.assertEqual(response.status_code, status.HTTP_201_CREATED)
+        task_run = TaskRun.objects.get(id=response.json()["id"])
+        self.assertEqual(task_run.state["model"], "gpt-5.6-terra")
+        self.assertEqual(task_run.state["reasoning_effort"], "high")
+        self.assertNotIn("runtime_adapter", task_run.state)
+
+    def test_create_run_endpoint_rejects_non_pi_thinking_level_for_pi_task(self):
+        task = self.create_task(runtime=Task.Runtime.PI)
+
+        response = self.client.post(
+            f"/api/projects/@current/tasks/{task.id}/runs/",
+            {
+                "environment": "cloud",
+                "mode": "interactive",
+                "model": "gpt-5.6-terra",
+                "reasoning_effort": "ultracode",
+            },
+            format="json",
+        )
+
+        self.assertEqual(response.status_code, status.HTTP_400_BAD_REQUEST)
+        self.assertIn("reasoning_effort", response.json())
+
     # is_url_allowed resolves DNS for real in CI, and example.com subdomains don't resolve.
     @patch("products.tasks.backend.presentation.serializers.is_url_allowed", return_value=(True, None))
     @patch("products.tasks.backend.temporal.client.execute_task_processing_workflow")