diff --git a/src/google/adk/evaluation/eval_metrics.py b/src/google/adk/evaluation/eval_metrics.py
index 09b483e2..79a587eb 100644
--- a/src/google/adk/evaluation/eval_metrics.py
+++ b/src/google/adk/evaluation/eval_metrics.py
@@ -23,6 +23,7 @@ from pydantic import alias_generators
 from pydantic import BaseModel
 from pydantic import ConfigDict
 from pydantic import Field
+from pydantic.json_schema import SkipJsonSchema
 from typing_extensions import TypeAlias
 
 from .common import EvalBaseModel
@@ -71,8 +72,10 @@ class JudgeModelOptions(EvalBaseModel):
       ),
   )
 
-  judge_model_config: Optional[genai_types.GenerateContentConfig] = Field(
-      default=genai_types.GenerateContentConfig,
+  judge_model_config: SkipJsonSchema[
+      Optional[genai_types.GenerateContentConfig]
+  ] = Field(
+      default=None,
       description="The configuration for the judge model.",
   )
 
diff --git a/src/google/adk/evaluation/hallucinations_v1.py b/src/google/adk/evaluation/hallucinations_v1.py
index cf03299f..587774a7 100644
--- a/src/google/adk/evaluation/hallucinations_v1.py
+++ b/src/google/adk/evaluation/hallucinations_v1.py
@@ -298,7 +298,10 @@ class HallucinationsV1Evaluator(Evaluator):
     self.segmenter_prompt = _HALLUCINATIONS_V1_SEGMENTER_PROMPT
     self.sentence_validator_prompt = _HALLUCINATIONS_V1_VALIDATOR_PROMPT
     self._model = self._judge_model_options.judge_model
-    self._model_config = self._judge_model_options.judge_model_config
+    self._model_config = (
+        self._judge_model_options.judge_model_config
+        or genai_types.GenerateContentConfig()
+    )
 
   def _setup_auto_rater(self) -> BaseLlm:
     model_id = self._judge_model_options.judge_model
diff --git a/src/google/adk/evaluation/llm_as_judge.py b/src/google/adk/evaluation/llm_as_judge.py
index 633caeff..226884d3 100644
--- a/src/google/adk/evaluation/llm_as_judge.py
+++ b/src/google/adk/evaluation/llm_as_judge.py
@@ -141,7 +141,8 @@ class LlmAsJudge(Evaluator):
                   role="user",
               )
           ],
-          config=self._judge_model_options.judge_model_config,
+          config=self._judge_model_options.judge_model_config
+          or genai_types.GenerateContentConfig(),
       )
       add_default_retry_options_if_not_present(llm_request)
       num_samples = self._judge_model_options.num_samples