diff --git a/google/genai/_transformers.py b/google/genai/_transformers.py
index 6739647133..1ab19cd4fa 100644
--- a/google/genai/_transformers.py
+++ b/google/genai/_transformers.py
@@ -1397,3 +1397,4 @@ def t_is_vertex_embed_content_model(model: str) -> bool:
 
 def t_json_schema(origin: Any) -> Any:
   return origin
+
diff --git a/google/genai/models.py b/google/genai/models.py
index c597326eb5..2d5240a2dd 100644
--- a/google/genai/models.py
+++ b/google/genai/models.py
@@ -6251,6 +6251,9 @@ def generate_content(
       # The image shows a flat lay arrangement of freshly baked blueberry
       # scones.
     """
+    import collections.abc
+    if isinstance(contents, (collections.abc.Iterator, collections.abc.Generator)):
+      contents = list(contents)
 
     incompatible_tools_indexes = (
         _extra_utils.find_afc_incompatible_tool_indexes(config)
@@ -6431,6 +6434,9 @@ def generate_content_stream(
       # The image shows a flat lay arrangement of freshly baked blueberry
       # scones.
     """
+    import collections.abc
+    if isinstance(contents, (collections.abc.Iterator, collections.abc.Generator)):
+      contents = list(contents)
 
     incompatible_tools_indexes = (
         _extra_utils.find_afc_incompatible_tool_indexes(config)
@@ -8442,6 +8448,9 @@ async def generate_content(
       print(response.text)
       # J'aime les bagels.
     """
+    import collections.abc
+    if isinstance(contents, (collections.abc.Iterator, collections.abc.Generator)):
+      contents = list(contents)
     # Retrieve and cache any MCP sessions if provided.
     incompatible_tools_indexes = (
         _extra_utils.find_afc_incompatible_tool_indexes(
@@ -8694,6 +8703,9 @@ async def generate_content_stream(
       # The image shows a flat lay arrangement of freshly baked blueberry
       # scones.
     """
+    import collections.abc
+    if isinstance(contents, (collections.abc.Iterator, collections.abc.Generator)):
+      contents = list(contents)
     if not config:
       parsed_config = None
     elif isinstance(config, dict):
diff --git a/google/genai/tests/models/test_gc_continuation_token.py b/google/genai/tests/models/test_gc_continuation_token.py
index 46dcdfcc5c..f2722a0958 100644
--- a/google/genai/tests/models/test_gc_continuation_token.py
+++ b/google/genai/tests/models/test_gc_continuation_token.py
@@ -4141,3 +4141,25 @@ async def _hop(resp):
     last = chunks[-1].candidates[0]
     assert last.finish_reason == types.FinishReason.MAX_TOKENS
     assert last.continuation_token == b'tok_hop2_max_tokens'
+
+def test_generate_content_accepts_reversed_iterator(mock_api_client):
+  """reversed([...]) contents should be materialized before Pydantic validation."""
+  models_module = models.Models(mock_api_client)
+  contents = [
+      types.Content(role='user', parts=[types.Part(text='hello')]),
+      types.Content(role='user', parts=[types.Part(text='world')]),
+  ]
+  mock_api_client.request.return_value = {
+      'candidates': [{'content': {'role': 'model', 'parts': [{'text': 'ok'}]}, 'finish_reason': 'STOP'}]
+  }
+  with mock.patch.object(
+      models.Models,
+      '_generate_content_with_continuation',
+      return_value=types.GenerateContentResponse(
+          candidates=[types.Candidate(content=types.Content(role='model', parts=[types.Part(text='ok')]))]
+      ),
+  ) as mock_gc:
+    models_module.generate_content(model='gemini-2.5-pro', contents=reversed(contents))
+    called_contents = mock_gc.call_args.kwargs['contents']
+    assert isinstance(called_contents, list), 'reversed() should be materialized to a list'
+    assert len(called_contents) == 2