diff --git a/python/packages/core/agent_framework/_agents.py b/python/packages/core/agent_framework/_agents.py
index a3f4570b6e..afd3030f76 100644
--- a/python/packages/core/agent_framework/_agents.py
+++ b/python/packages/core/agent_framework/_agents.py
@@ -943,8 +943,13 @@ def _propagate_conversation_id(update: AgentResponseUpdate) -> AgentResponseUpda
                     map_chat_to_agent_update,
                     agent_name=self.name,
                 ),
-                finalizer=partial(
-                    self._finalize_response_updates, response_format=options.get("response_format") if options else None
+                finalizer=lambda updates: self._finalize_response_updates(
+                    updates,
+                    response_format=(
+                        ctx_holder["ctx"]["chat_options"].get("response_format")
+                        if ctx_holder["ctx"]
+                        else (options.get("response_format") if options else None)
+                    ),
                 ),
             )
             .with_transform_hook(_propagate_conversation_id)
diff --git a/python/packages/core/tests/core/test_agents.py b/python/packages/core/tests/core/test_agents.py
index 627987a1f2..e49666b5eb 100644
--- a/python/packages/core/tests/core/test_agents.py
+++ b/python/packages/core/tests/core/test_agents.py
@@ -97,6 +97,32 @@ async def test_chat_client_agent_run_streaming(client: SupportsChatGetResponse)
     assert result.text == "test streaming response another update"
 
 
+async def test_chat_client_agent_run_streaming_with_default_response_format(client: SupportsChatGetResponse) -> None:
+    """Test that response_format set via default_options produces a parsed value when streaming."""
+    from pydantic import BaseModel
+
+    class Greeting(BaseModel):
+        greeting: str
+
+    # Configure streaming responses to return valid JSON for the model
+    client.streaming_responses = [  # type: ignore[attr-defined]
+        [
+            ChatResponseUpdate(contents=[Content.from_text('{"greeting": "Hello"}')], role="assistant"),
+        ]
+    ]
+
+    agent = Agent(client=client, default_options={"response_format": Greeting})
+    stream = agent.run("Hello", stream=True)
+    async for _ in stream:
+        pass
+    result = await stream.get_final_response()
+
+    assert result.text == '{"greeting": "Hello"}'
+    assert result.value is not None
+    assert isinstance(result.value, Greeting)
+    assert result.value.greeting == "Hello"
+
+
 async def test_chat_client_agent_create_session(client: SupportsChatGetResponse) -> None:
     agent = Agent(client=client)
     session = agent.create_session()