diff --git a/tests/integration/test_end_to_end.py b/tests/integration/test_end_to_end.py
index 58dce528d..aea9784ad 100644
--- a/tests/integration/test_end_to_end.py
+++ b/tests/integration/test_end_to_end.py
@@ -5,15 +5,20 @@
 import httpx
 import pytest
 import pytest_asyncio
+
 from starlette.applications import Starlette
 
 from a2a.client.base_client import BaseClient
-from a2a.client.client import ClientConfig
+from a2a.client.client import ClientCallContext, ClientConfig
 from a2a.client.client_factory import ClientFactory
+from a2a.client.service_parameters import (
+    ServiceParametersFactory,
+    with_a2a_extensions,
+)
 from a2a.server.agent_execution import AgentExecutor, RequestContext
 from a2a.server.events import EventQueue
 from a2a.server.events.in_memory_queue_manager import InMemoryQueueManager
-from a2a.server.request_handlers import GrpcHandler, DefaultRequestHandler
+from a2a.server.request_handlers import DefaultRequestHandler, GrpcHandler
 from a2a.server.routes import create_agent_card_routes, create_jsonrpc_routes
 from a2a.server.routes.rest_routes import create_rest_routes
 from a2a.server.tasks import TaskUpdater
@@ -21,6 +26,7 @@
 from a2a.types import (
     AgentCapabilities,
     AgentCard,
+    AgentExtension,
     AgentInterface,
     CancelTaskRequest,
     DeleteTaskPushNotificationConfigRequest,
@@ -41,6 +47,12 @@
 from a2a.utils.errors import InvalidParamsError
 
 
+SUPPORTED_EXTENSION_URIS = [
+    'https://example.com/ext/v1',
+    'https://example.com/ext/v2',
+]
+
+
 def assert_message_matches(message, expected_role, expected_text):
     assert message.role == expected_role
     assert message.parts[0].text == expected_text
@@ -87,6 +99,23 @@ class MockAgentExecutor(AgentExecutor):
     async def execute(self, context: RequestContext, event_queue: EventQueue):
         user_input = context.get_user_input()
 
+        # Extensions echo: activate all requested extensions and report them
+        # back via the Message.extensions field.
+        if user_input.startswith('Extensions:'):
+            for ext_uri in context.requested_extensions:
+                context.add_activated_extension(ext_uri)
+            await event_queue.enqueue_event(
+                Message(
+                    role=Role.ROLE_AGENT,
+                    message_id='ext-reply-1',
+                    parts=[Part(text='extensions echoed')],
+                    extensions=sorted(
+                        context.call_context.activated_extensions
+                    ),
+                )
+            )
+            return
+
         # Direct message response (no task created).
         if user_input.startswith('Message:'):
             await event_queue.enqueue_event(
@@ -142,7 +171,15 @@ def agent_card() -> AgentCard:
         description='Real in-memory integration testing.',
         version='1.0.0',
         capabilities=AgentCapabilities(
-            streaming=True, push_notifications=False
+            streaming=True,
+            push_notifications=False,
+            extensions=[
+                AgentExtension(
+                    uri=uri,
+                    description=f'Test extension {uri}',
+                )
+                for uri in SUPPORTED_EXTENSION_URIS
+            ],
         ),
         skills=[],
         default_input_modes=['text/plain'],
@@ -757,3 +794,44 @@ async def test_end_to_end_direct_message_return_immediately(transport_setups):
         Role.ROLE_AGENT,
         'Direct reply to: Message: Quick question',
     )
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    'streaming',
+    [
+        pytest.param(False, id='blocking'),
+        pytest.param(True, id='streaming'),
+    ],
+)
+async def test_end_to_end_extensions_propagation(transport_setups, streaming):
+    """Test that extensions sent by the client reach the agent executor."""
+    client = transport_setups.client
+    client._config.streaming = streaming
+
+    service_params = ServiceParametersFactory.create(
+        [with_a2a_extensions(SUPPORTED_EXTENSION_URIS)]
+    )
+    context = ClientCallContext(service_parameters=service_params)
+
+    message_to_send = Message(
+        role=Role.ROLE_USER,
+        message_id='msg-ext-propagation',
+        parts=[Part(text='Extensions: echo')],
+    )
+
+    events = [
+        event
+        async for event in client.send_message(
+            request=SendMessageRequest(message=message_to_send),
+            context=context,
+        )
+    ]
+
+    assert len(events) == 1
+    response = events[0]
+    assert response.HasField('message')
+    assert_message_matches(
+        response.message, Role.ROLE_AGENT, 'extensions echoed'
+    )
+    assert set(response.message.extensions) == set(SUPPORTED_EXTENSION_URIS)