fix: use Gemini 3+ check for native output_schema + tools support

can_use_output_schema_with_tools() was using is_gemini_2_or_above(),
which incorrectly enabled native response_schema + tools for all
Gemini 2.x models on Vertex AI. Gemini 2.0/2.5 can't actually handle
both constraints at the same time — the model just keeps firing tool
calls and never produces the structured response, resulting in an
infinite loop.

Per Google's docs, structured output combined with tools is only
supported on Gemini 3 series models. This change adds
is_gemini_3_or_above() and uses it so that Gemini 2.x falls back
to the SetModelResponseTool workaround (which works fine).

Author: vietnamesekid

src/google/adk/utils/model_name_utils.py

@@ -125,3 +125,31 @@ def is_gemini_2_or_above(model_string: Optional[str]) -> bool:
     return False
 
   return parsed_version.major >= 2
+
+
+def is_gemini_3_or_above(model_string: Optional[str]) -> bool:
+  """Check if the model is a Gemini 3.0 or newer model using semantic versions.
+
+  Args:
+    model_string: Either a simple model name or path-based model name
+
+  Returns:
+    True if it's a Gemini 3.0+ model, False otherwise
+  """
+  if not model_string:
+    return False
+
+  model_name = extract_model_name(model_string)
+  if not model_name.startswith('gemini-'):
+    return False
+
+  version_string = model_name[len('gemini-'):].split('-', 1)[0]
+  if not version_string:
+    return False
+
+  try:
+    parsed_version = Version(version_string)
+  except InvalidVersion:
+    return False
+
+  return parsed_version.major >= 3

src/google/adk/utils/output_schema_utils.py

@@ -23,7 +23,7 @@
 from typing import Union
 
 from ..models.base_llm import BaseLlm
-from .model_name_utils import is_gemini_2_or_above
+from .model_name_utils import is_gemini_3_or_above
 from .variant_utils import get_google_llm_variant
 from .variant_utils import GoogleLLMVariant
 
@@ -49,5 +49,5 @@ def can_use_output_schema_with_tools(model: Union[str, BaseLlm]) -> bool:
 
   return (
       get_google_llm_variant() == GoogleLLMVariant.VERTEX_AI
-      and is_gemini_2_or_above(model_string)
+      and is_gemini_3_or_above(model_string)
   )

tests/unittests/utils/test_model_name_utils.py

@@ -17,6 +17,7 @@
 from google.adk.utils.model_name_utils import extract_model_name
 from google.adk.utils.model_name_utils import is_gemini_1_model
 from google.adk.utils.model_name_utils import is_gemini_2_or_above
+from google.adk.utils.model_name_utils import is_gemini_3_or_above
 from google.adk.utils.model_name_utils import is_gemini_model
 from google.adk.utils.model_name_utils import is_gemini_model_id_check_disabled
 
@@ -236,6 +237,40 @@ def test_is_gemini_2_or_above_edge_cases(self):
     assert is_gemini_2_or_above('gemini-one') is False
 
 
+class TestIsGemini3OrAbove:
+  """Test the is_gemini_3_or_above function."""
+
+  def test_is_gemini_3_or_above_simple_names(self):
+    """Test Gemini 3.0+ model detection with simple model names."""
+    assert is_gemini_3_or_above('gemini-3.0-pro') is True
+    assert is_gemini_3_or_above('gemini-3.1-pro-preview') is True
+    assert is_gemini_3_or_above('gemini-3-flash-preview') is True
+    assert is_gemini_3_or_above('gemini-4.0-pro') is True
+    assert is_gemini_3_or_above('gemini-2.5-pro') is False
+    assert is_gemini_3_or_above('gemini-2.0-flash') is False
+    assert is_gemini_3_or_above('gemini-1.5-flash') is False
+    assert is_gemini_3_or_above('claude-3-sonnet') is False
+
+  def test_is_gemini_3_or_above_path_based_names(self):
+    """Test Gemini 3.0+ model detection with path-based model names."""
+    gemini_3_path = 'projects/12345/locations/us-east1/publishers/google/models/gemini-3.0-pro'
+    assert is_gemini_3_or_above(gemini_3_path) is True
+
+    gemini_3_path_2 = 'projects/12345/locations/us-east1/publishers/google/models/gemini-3.1-pro-preview'
+    assert is_gemini_3_or_above(gemini_3_path_2) is True
+
+    gemini_2_path = 'projects/265104255505/locations/us-central1/publishers/google/models/gemini-2.5-pro'
+    assert is_gemini_3_or_above(gemini_2_path) is False
+
+  def test_is_gemini_3_or_above_edge_cases(self):
+    """Test edge cases for Gemini 3.0+ model detection."""
+    assert is_gemini_3_or_above(None) is False
+    assert is_gemini_3_or_above('') is False
+    assert is_gemini_3_or_above('gemini-3.') is False
+    assert is_gemini_3_or_above('gemini-one') is False
+    assert is_gemini_3_or_above('my-gemini-3.0-model') is False
+
+
 class TestModelNameUtilsIntegration:
   """Integration tests for model name utilities."""
 

tests/unittests/utils/test_output_schema_utils.py

@@ -29,13 +29,19 @@
 @pytest.mark.parametrize(
     "model, env_value, expected",
     [
-        ("gemini-2.5-pro", "1", True),
+        ("gemini-3.1-pro", "1", True),
+        ("gemini-3.1-pro", "0", False),
+        ("gemini-3.1-pro", None, False),
+        (Gemini(model="gemini-3.0-flash"), "1", True),
+        (Gemini(model="gemini-3.0-flash"), "0", False),
+        (Gemini(model="gemini-3.0-flash"), None, False),
+        ("gemini-2.5-pro", "1", False),
         ("gemini-2.5-pro", "0", False),
         ("gemini-2.5-pro", None, False),
-        (Gemini(model="gemini-2.5-pro"), "1", True),
+        (Gemini(model="gemini-2.5-pro"), "1", False),
         (Gemini(model="gemini-2.5-pro"), "0", False),
         (Gemini(model="gemini-2.5-pro"), None, False),
-        ("gemini-2.0-flash", "1", True),
+        ("gemini-2.0-flash", "1", False),
         ("gemini-2.0-flash", "0", False),
         ("gemini-2.0-flash", None, False),
         ("gemini-1.5-pro", "1", False),