diff --git a/google/genai/_automatic_function_calling_util.py b/google/genai/_automatic_function_calling_util.py
index ecc9258e12..9cbc50ffcd 100644
--- a/google/genai/_automatic_function_calling_util.py
+++ b/google/genai/_automatic_function_calling_util.py
@@ -347,7 +347,7 @@ def parse_function_declaration_json_schema(
     behavior: Optional[types.Behavior]
     ) -> types.FunctionDeclaration:
   """Parse function declaration JSON schema from a callable."""
-  annotation_under_future = typing.get_type_hints(callable)
+  annotation_under_future = typing.get_type_hints(callable, include_extras=True)
   parameters_properties_json_schema = {}
   root_defs = {}
 
diff --git a/google/genai/_extra_utils.py b/google/genai/_extra_utils.py
index fe118d98c1..8844908c69 100644
--- a/google/genai/_extra_utils.py
+++ b/google/genai/_extra_utils.py
@@ -312,12 +312,20 @@ def convert_argument_from_function(
 ) -> _common.StringDict:
   signature = inspect.signature(function)
   func_name = function.__name__
+  # Without include_extras, Annotated[T, ...] unwraps to runtime type T.
+  try:
+    type_hints = typing.get_type_hints(function)
+  except (NameError, TypeError):
+    type_hints = {}
   converted_args = {}
   for param_name, param in signature.parameters.items():
     if param_name in args:
+      annotation = param.annotation
+      if isinstance(annotation, str) and param_name in type_hints:
+        annotation = type_hints[param_name]
       converted_args[param_name] = convert_if_exist_pydantic_model(
           args[param_name],
-          param.annotation,
+          annotation,
           param_name,
           func_name,
       )
diff --git a/google/genai/tests/afc/test_future_annotations.py b/google/genai/tests/afc/test_future_annotations.py
new file mode 100644
index 0000000000..e1f7a89e2f
--- /dev/null
+++ b/google/genai/tests/afc/test_future_annotations.py
@@ -0,0 +1,150 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+"""Tests for invoking AFC functions defined under PEP 563 annotations."""
+
+# !Please DO NOT combine the test in this file with other tests. This file is
+# used to test the future annotation, which is the first line of import.
+from __future__ import annotations
+
+import typing
+from typing import Annotated, Optional
+
+import pydantic
+import pytest
+
+from ... import _extra_utils
+from ... import errors
+from ... import types
+
+if typing.TYPE_CHECKING:
+  from ...client import Client
+
+
+class Location(pydantic.BaseModel):
+  city: str
+
+
+def _response_with_call(name: str, args: dict[str, object]):
+  return types.GenerateContentResponse(
+      candidates=[
+          types.Candidate(
+              content=types.Content(
+                  parts=[
+                      types.Part(
+                          function_call=types.FunctionCall(name=name, args=args)
+                      )
+                  ]
+              )
+          )
+      ]
+  )
+
+
+def test_invoke_builtin_primitive_types():
+  """String annotations of builtin types resolve before the type check."""
+
+  def get_weather(city: str, days: int = 3) -> str:
+    return f'sunny in {city} for {days} days'
+
+  result = _extra_utils.invoke_function_from_dict_args(
+      {'city': 'Paris', 'days': 2}, get_weather
+  )
+
+  assert result == 'sunny in Paris for 2 days'
+
+
+def test_get_function_response_parts_runs_tool():
+  """The tool runs and its result, not a TypeError, goes to the model."""
+
+  def get_weather(city: str) -> str:
+    return f'sunny in {city}'
+
+  parts = _extra_utils.get_function_response_parts(
+      _response_with_call('get_weather', {'city': 'Paris'}),
+      {'get_weather': get_weather},
+  )
+
+  assert parts[0].function_response.response == {'result': 'sunny in Paris'}
+
+
+def test_invoke_pydantic_model_and_containers():
+  """Pydantic models, lists of them and Optional resolve from strings."""
+
+  def find(
+      location: Location,
+      locations: list[Location],
+      days: Optional[int] = None,
+  ) -> list[object]:
+    return [location, locations, days]
+
+  location, locations, days = _extra_utils.invoke_function_from_dict_args(
+      {
+          'location': {'city': 'Paris'},
+          'locations': [{'city': 'Rome'}, {'city': 'Oslo'}],
+          'days': 2,
+      },
+      find,
+  )
+
+  assert location == Location(city='Paris')
+  assert locations == [Location(city='Rome'), Location(city='Oslo')]
+  assert days == 2
+
+
+def test_invoke_annotated_parameter():
+  """An Annotated string annotation checks the value against its base type."""
+
+  def forecast(days: Annotated[int, pydantic.Field(ge=1, le=7)] = 3) -> int:
+    return days
+
+  assert _extra_utils.invoke_function_from_dict_args({'days': 2}, forecast) == 2
+
+
+def test_invoke_incompatible_value_raises():
+  """A mismatched value raises the same error as with eager annotations."""
+
+  def get_weather(city: str) -> str:
+    return city
+
+  with pytest.raises(
+      errors.UnknownFunctionCallArgumentError, match='not compatible'
+  ):
+    _extra_utils.invoke_function_from_dict_args({'city': 1}, get_weather)
+
+
+def test_invoke_unresolvable_hints_falls_back_to_raw_annotations():
+  """A TYPE_CHECKING-only name does not raise NameError from the lookup."""
+
+  def forecast(days: int = 3, client: Optional[Client] = None) -> int:
+    del client
+    return days
+
+  assert _extra_utils.invoke_function_from_dict_args({}, forecast) == 3
+
+
+@pytest.mark.asyncio
+async def test_get_function_response_parts_async_runs_tool():
+  """The async path runs a coroutine tool defined under PEP 563."""
+
+  async def get_weather(city: str) -> str:
+    return f'sunny in {city}'
+
+  parts = await _extra_utils.get_function_response_parts_async(
+      _response_with_call('get_weather', {'city': 'Paris'}),
+      {'get_weather': get_weather},
+  )
+
+  assert parts[0].function_response.response == {'result': 'sunny in Paris'}
diff --git a/google/genai/tests/types/test_future.py b/google/genai/tests/types/test_future.py
index dc5eb597cb..386e5e53d6 100644
--- a/google/genai/tests/types/test_future.py
+++ b/google/genai/tests/types/test_future.py
@@ -18,6 +18,8 @@
 from __future__ import annotations
 
 import copy
+from typing import Annotated
+
 import pydantic
 
 from ... import types
@@ -99,3 +101,27 @@ def func_under_test(param_1: ComplexType, param_2: int) -> str:
 
   assert actual_schema_mldev == expected_schema_mldev
   assert actual_schema_vertex == expected_schema_vertex
+
+
+def test_future_annotation_annotated_metadata_json_schema():
+  """The JSON schema keeps Annotated metadata from string annotations."""
+
+  def func_under_test(
+      days: Annotated[
+          int,
+          pydantic.Field(description='Forecast length in days', ge=1, le=7),
+      ] = 3,
+  ) -> str:
+    return '123'
+
+  actual_schema = types.FunctionDeclaration.from_callable(
+      client=mldev_client, callable=func_under_test, use_json_schema=True
+  )
+
+  assert actual_schema.parameters_json_schema['properties']['days'] == {
+      'description': 'Forecast length in days',
+      'maximum': 7,
+      'minimum': 1,
+      'type': 'integer',
+      'default': 3,
+  }