fix: warn on deprecated Gemini model alias

src/google/adk/models/registry.py

@@ -31,6 +31,9 @@
 
 _LazyEntry = tuple[str, str]
 _llm_registry_dict: dict[str, Union[type['BaseLlm'], _LazyEntry]] = {}
+_deprecated_model_aliases = {
+    'gemini-flash-latest': 'gemini-2.5-flash',
+}
 
 
 class LLMRegistry:
@@ -48,6 +51,7 @@ def new_llm(model: str) -> BaseLlm:
     """
 
     prefix, actual_model = LLMRegistry._parse_model(model)
+    LLMRegistry._warn_if_deprecated_alias(actual_model)
     cls = LLMRegistry.resolve(model)
 
     if prefix and LLMRegistry._match_prefix(prefix, cls.__name__):
@@ -67,6 +71,21 @@ def _parse_model(model: str) -> tuple[str | None, str]:
       return prefix, actual_model
     return None, model
 
+  @staticmethod
+  def _warn_if_deprecated_alias(model: str) -> None:
+    replacement = _deprecated_model_aliases.get(model)
+    if replacement is None:
+      return
+
+    logger.warning(
+        (
+            'Model alias %r is deprecated and may resolve to an unavailable'
+            ' Gemini model. Use %r or another versioned model id instead.'
+        ),
+        model,
+        replacement,
+    )
+
   @staticmethod
   def _match_prefix(prefix: str, class_name: str) -> bool:
     """Checks if a prefix matches a class name."""

tests/unittests/models/test_models.py

@@ -133,6 +133,22 @@ def test_new_llm_with_prefix(mocker):
   mock_class.assert_called_once_with(model='gpt-4')
 
 
+@pytest.mark.parametrize(
+    'model_name',
+    ['gemini-flash-latest', 'gemini:gemini-flash-latest'],
+)
+def test_new_llm_warns_for_deprecated_model_alias(caplog, model_name):
+  """Test that deprecated Gemini aliases surface a useful warning."""
+  caplog.set_level('WARNING', logger='google_adk.google.adk.models.registry')
+
+  llm = models.LLMRegistry.new_llm(model_name)
+
+  assert isinstance(llm, Gemini)
+  assert llm.model == 'gemini-flash-latest'
+  assert "Model alias 'gemini-flash-latest' is deprecated" in caplog.text
+  assert "'gemini-2.5-flash'" in caplog.text
+
+
 def test_new_llm_with_non_matching_prefix(mocker):
   """Test that new_llm keeps prefix if it does not match class."""
   mock_class = mocker.MagicMock()