diff --git a/rdagent/oai/backend/base.py b/rdagent/oai/backend/base.py
index 5a0b83ce..c9a5789a 100644
--- a/rdagent/oai/backend/base.py
+++ b/rdagent/oai/backend/base.py
@@ -378,7 +378,7 @@ class APIBackend(ABC):
 
         all_response = ""
         new_messages = deepcopy(messages)
-        for _ in range(3):
+        for _ in range(6):  # for some long code, 3 times may not enough for reasoning models
             if "json_mode" in kwargs:
                 del kwargs["json_mode"]
             response, finish_reason = self._create_chat_completion_add_json_in_prompt(
diff --git a/rdagent/scenarios/data_science/proposal/exp_gen.py b/rdagent/scenarios/data_science/proposal/exp_gen.py
index 8c3dcdb1..96de6361 100644
--- a/rdagent/scenarios/data_science/proposal/exp_gen.py
+++ b/rdagent/scenarios/data_science/proposal/exp_gen.py
@@ -420,7 +420,10 @@ class DSExpGen(ExpGen):
                             user_prompt=user_prompt,
                             system_prompt=system_prompt,
                             json_mode=True,
-                            json_target_type=dict[str, dict[str, str] | str],  # workflow_update may be a string
+                            # NOTE: corner cases.
+                            # workflow_update may be a string
+                            # model could have 2 level nested dict.
+                            json_target_type=dict[str, dict[str, str | dict] | str],
                         )
                     )
                     assert "hypothesis_proposal" in resp_dict, "Hypothesis proposal not provided."