diff --git a/astrbot/core/provider/sources/gemini_source.py b/astrbot/core/provider/sources/gemini_source.py
index f4cba79805..4cbb40fcec 100644
--- a/astrbot/core/provider/sources/gemini_source.py
+++ b/astrbot/core/provider/sources/gemini_source.py
@@ -251,17 +251,22 @@ async def _prepare_query_config(
             )
             if thinking_level and isinstance(thinking_level, str):
                 thinking_level = thinking_level.upper()
-                if thinking_level not in ["MINIMAL", "LOW", "MEDIUM", "HIGH"]:
+                allowed_levels = {"MINIMAL", "LOW", "MEDIUM", "HIGH"}
+                fallback_level = "HIGH"
+                if model_name.startswith("gemini-3.7"):
+                    allowed_levels = {"LOW", "MEDIUM", "HIGH"}
+                    fallback_level = "MEDIUM"
+                if thinking_level not in allowed_levels:
                     logger.warning(
-                        f"Invalid thinking level: {thinking_level}, using HIGH"
+                        "Invalid thinking level %s for %s, using %s",
+                        thinking_level,
+                        model_name,
+                        fallback_level,
                     )
-                    thinking_level = "HIGH"
-                level = types.ThinkingLevel(thinking_level)
-                thinking_config = types.ThinkingConfig()
-                if not hasattr(types.ThinkingConfig, "thinking_level"):
-                    setattr(types.ThinkingConfig, "thinking_level", level)
-                else:
-                    thinking_config.thinking_level = level
+                    thinking_level = fallback_level
+                thinking_config = types.ThinkingConfig(
+                    thinking_level=types.ThinkingLevel(thinking_level)
+                )
 
         return types.GenerateContentConfig(
             system_instruction=system_instruction,
diff --git a/tests/test_gemini_source.py b/tests/test_gemini_source.py
index 4c33de6bca..b5464e8047 100644
--- a/tests/test_gemini_source.py
+++ b/tests/test_gemini_source.py
@@ -10,6 +10,45 @@
 from astrbot.core.provider.sources.gemini_source import ProviderGoogleGenAI
 
 
+@pytest.mark.asyncio
+async def test_gemini_thinking_level_is_serialized_on_every_request():
+    model = "gemini-3.7-flash"
+    provider = ProviderGoogleGenAI.__new__(ProviderGoogleGenAI)
+    provider.provider_config = {"gm_thinking_config": {"level": "HIGH"}}
+    provider.provider_settings = {}
+    provider.model_name = model
+    provider.safety_settings = []
+
+    first_config = await provider._prepare_query_config({"model": model})
+    second_config = await provider._prepare_query_config({"model": model})
+
+    assert first_config.thinking_config is not None
+    assert second_config.thinking_config is not None
+    assert first_config.thinking_config.model_dump(exclude_none=True) == {
+        "thinking_level": types.ThinkingLevel.HIGH,
+    }
+    assert second_config.thinking_config.model_dump(exclude_none=True) == {
+        "thinking_level": types.ThinkingLevel.HIGH,
+    }
+
+
+@pytest.mark.asyncio
+async def test_gemini_37_minimal_thinking_level_falls_back_to_medium():
+    model = "gemini-3.7-flash"
+    provider = ProviderGoogleGenAI.__new__(ProviderGoogleGenAI)
+    provider.provider_config = {"gm_thinking_config": {"level": "MINIMAL"}}
+    provider.provider_settings = {}
+    provider.model_name = model
+    provider.safety_settings = []
+
+    config = await provider._prepare_query_config({"model": model})
+
+    assert config.thinking_config is not None
+    assert config.thinking_config.model_dump(exclude_none=True) == {
+        "thinking_level": types.ThinkingLevel.MEDIUM,
+    }
+
+
 @pytest.mark.asyncio
 async def test_gemini_prepare_conversation_removes_leading_model_content():
     provider = ProviderGoogleGenAI.__new__(ProviderGoogleGenAI)