diff --git a/gradient_adk/decorator.py b/gradient_adk/decorator.py
index da70631..8031eda 100644
--- a/gradient_adk/decorator.py
+++ b/gradient_adk/decorator.py
@@ -166,7 +166,49 @@ async def run(req: Request):
                 logger.error("Error creating generator", error=str(e), exc_info=True)
                 raise HTTPException(status_code=500, detail="Internal server error")
 
-            # Wrap in tracking iterator
+            # If evaluation mode, collect all chunks and return as single response with trace ID
+            if is_evaluation:
+                from fastapi.responses import JSONResponse
+
+                collected_chunks: List[str] = []
+                try:
+                    async for chunk in user_gen:
+                        if isinstance(chunk, bytes):
+                            chunk_str = chunk.decode("utf-8", errors="replace")
+                        elif isinstance(chunk, dict):
+                            chunk_str = json.dumps(chunk)
+                        elif chunk is None:
+                            continue
+                        else:
+                            chunk_str = str(chunk)
+                        collected_chunks.append(chunk_str)
+
+                    result = "".join(collected_chunks)
+
+                    # Submit tracking and get trace ID
+                    trace_id = None
+                    if tr:
+                        try:
+                            tr._req["outputs"] = result
+                            trace_id = await tr.submit_and_get_trace_id()
+                        except Exception:
+                            pass
+
+                    headers = {"X-Gradient-Trace-Id": trace_id} if trace_id else {}
+                    return JSONResponse(content=result, headers=headers)
+
+                except Exception as e:
+                    if tr:
+                        try:
+                            tr._req["outputs"] = "".join(collected_chunks)
+                            tr._req["error"] = str(e)
+                            await tr._submit()
+                        except Exception:
+                            pass
+                    logger.error("Error in streaming evaluation", error=str(e), exc_info=True)
+                    raise HTTPException(status_code=500, detail="Internal server error")
+
+            # Normal streaming case - wrap in tracking iterator
             streaming_iter = _StreamingIteratorWithTracking(user_gen, tr, func.__name__)
 
             return FastAPIStreamingResponse(
@@ -234,4 +276,4 @@ async def health():
 
 def run_server(fastapi_app: FastAPI, host: str = "0.0.0.0", port: int = 8080, **kwargs):
     """Run the FastAPI server with uvicorn."""
-    uvicorn.run(fastapi_app, host=host, port=port, **kwargs)
+    uvicorn.run(fastapi_app, host=host, port=port, **kwargs)
\ No newline at end of file
diff --git a/integration_tests/example_agents/streaming_echo_agent/main.py b/integration_tests/example_agents/streaming_echo_agent/main.py
new file mode 100644
index 0000000..4750d09
--- /dev/null
+++ b/integration_tests/example_agents/streaming_echo_agent/main.py
@@ -0,0 +1,17 @@
+"""
+Streaming echo agent for integration testing.
+Does not make any external API calls - just echoes back the input in chunks.
+Used to test streaming vs non-streaming behavior with evaluation-id header.
+"""
+
+from gradient_adk import entrypoint
+
+
+@entrypoint
+async def main(query, context):
+    """Streaming echo agent - yields the response in chunks."""
+    prompt = query.get("prompt", "no prompt provided")
+    # Stream the response in multiple chunks
+    yield "Echo: "
+    yield prompt
+    yield " [DONE]"
\ No newline at end of file
diff --git a/integration_tests/run/test_adk_agents_run.py b/integration_tests/run/test_adk_agents_run.py
index 156cb08..fc48232 100644
--- a/integration_tests/run/test_adk_agents_run.py
+++ b/integration_tests/run/test_adk_agents_run.py
@@ -59,6 +59,11 @@ def echo_agent_dir(self):
         """Get the path to the echo agent directory."""
         return Path(__file__).parent.parent / "example_agents" / "echo_agent"
 
+    @pytest.fixture
+    def streaming_echo_agent_dir(self):
+        """Get the path to the streaming echo agent directory."""
+        return Path(__file__).parent.parent / "example_agents" / "streaming_echo_agent"
+
     @pytest.fixture
     def setup_agent_in_temp(self, echo_agent_dir):
         """
@@ -86,6 +91,33 @@ def setup_agent_in_temp(self, echo_agent_dir):
 
             yield temp_path
 
+    @pytest.fixture
+    def setup_streaming_agent_in_temp(self, streaming_echo_agent_dir):
+        """
+        Setup a temporary directory with the streaming echo agent and proper configuration.
+        Yields the temp directory path and cleans up after.
+        """
+        with tempfile.TemporaryDirectory() as temp_dir:
+            temp_path = Path(temp_dir)
+
+            # Copy the streaming echo agent main.py
+            shutil.copy(streaming_echo_agent_dir / "main.py", temp_path / "main.py")
+
+            # Create .gradient directory and config
+            gradient_dir = temp_path / ".gradient"
+            gradient_dir.mkdir()
+
+            config = {
+                "agent_name": "test-streaming-echo-agent",
+                "agent_environment": "main",
+                "entrypoint_file": "main.py",
+            }
+
+            with open(gradient_dir / "agent.yml", "w") as f:
+                yaml.safe_dump(config, f)
+
+            yield temp_path
+
     @pytest.mark.cli
     def test_agent_run_happy_path(self, setup_agent_in_temp):
         """
@@ -386,5 +418,135 @@ def test_agent_run_run_endpoint_with_various_inputs(self, setup_agent_in_temp):
             assert data["echo"] == "Hello `} E1-('"
             logger.info("Unicode test passed")
 
+        finally:
+            cleanup_process(process)
+
+    @pytest.mark.cli
+    def test_streaming_agent_without_evaluation_id_streams_response(
+        self, setup_streaming_agent_in_temp
+    ):
+        """
+        Test that a streaming agent returns a streamed response when no evaluation-id header is sent.
+        Verifies:
+        - Response is streamed (text/event-stream content type)
+        - Response contains the expected content
+        """
+        logger = logging.getLogger(__name__)
+        temp_dir = setup_streaming_agent_in_temp
+        port = find_free_port()
+        process = None
+
+        try:
+            logger.info(f"Starting streaming agent on port {port} in {temp_dir}")
+
+            # Start the agent server
+            process = subprocess.Popen(
+                [
+                    "gradient",
+                    "agent",
+                    "run",
+                    "--port",
+                    str(port),
+                    "--no-dev",
+                ],
+                cwd=temp_dir,
+                start_new_session=True,
+            )
+
+            # Wait for server to be ready
+            server_ready = wait_for_server(port, timeout=30)
+            assert server_ready, "Server did not start within timeout"
+
+            # Make a streaming request WITHOUT evaluation-id header
+            with requests.post(
+                f"http://localhost:{port}/run",
+                json={"prompt": "Hello, World!"},
+                stream=True,
+                timeout=30,
+            ) as response:
+                assert response.status_code == 200
+
+                # Verify it's a streaming response (text/event-stream)
+                content_type = response.headers.get("content-type", "")
+                assert "text/event-stream" in content_type, (
+                    f"Expected text/event-stream content type for streaming, got: {content_type}"
+                )
+
+                # Collect chunks to verify content
+                chunks = list(response.iter_content(decode_unicode=True))
+                full_content = "".join(c for c in chunks if c)
+
+                # Verify the content contains the expected streamed output
+                assert "Echo:" in full_content or "Hello, World!" in full_content, (
+                    f"Expected streamed content to contain prompt, got: {full_content}"
+                )
+
+                logger.info(f"Streaming response received with {len(chunks)} chunks")
+                logger.info(f"Full content: {full_content}")
+
+        finally:
+            cleanup_process(process)
+
+    @pytest.mark.cli
+    def test_streaming_agent_with_evaluation_id_returns_single_response(
+        self, setup_streaming_agent_in_temp
+    ):
+        """
+        Test that a streaming agent returns a single JSON response (not streamed)
+        when the evaluation-id header is present.
+        Verifies:
+        - Response is NOT streamed (application/json content type)
+        - Response contains the complete collected content
+        """
+        logger = logging.getLogger(__name__)
+        temp_dir = setup_streaming_agent_in_temp
+        port = find_free_port()
+        process = None
+
+        try:
+            logger.info(f"Starting streaming agent on port {port} in {temp_dir}")
+
+            # Start the agent server
+            process = subprocess.Popen(
+                [
+                    "gradient",
+                    "agent",
+                    "run",
+                    "--port",
+                    str(port),
+                    "--no-dev",
+                ],
+                cwd=temp_dir,
+                start_new_session=True,
+            )
+
+            # Wait for server to be ready
+            server_ready = wait_for_server(port, timeout=30)
+            assert server_ready, "Server did not start within timeout"
+
+            # Make a request WITH evaluation-id header
+            response = requests.post(
+                f"http://localhost:{port}/run",
+                json={"prompt": "Hello, World!"},
+                headers={"evaluation-id": "test-eval-123"},
+                timeout=30,
+            )
+            assert response.status_code == 200
+
+            # Verify it's NOT a streaming response (should be application/json)
+            content_type = response.headers.get("content-type", "")
+            assert "application/json" in content_type, (
+                f"Expected application/json content type for evaluation mode, got: {content_type}"
+            )
+
+            # Verify the response contains the complete content
+            result = response.json()
+            expected_content = "Echo: Hello, World! [DONE]"
+            assert result == expected_content, (
+                f"Expected complete collected content '{expected_content}', got: {result}"
+            )
+
+            logger.info(f"Single JSON response received: {result}")
+
         finally:
             cleanup_process(process)
\ No newline at end of file
diff --git a/tests/decorator_test.py b/tests/decorator_test.py
index 9d993cc..6a16d0e 100644
--- a/tests/decorator_test.py
+++ b/tests/decorator_test.py
@@ -31,6 +31,7 @@ def __init__(self):
         self.ended = []
         self.closed = False
         self._req = {}
+        self._submitted_trace_id = None
 
     def on_request_start(self, name, inputs, is_evaluation=False):
         self.started.append((name, inputs, is_evaluation))
@@ -45,6 +46,12 @@ async def _submit(self):
         """Simulate async submission."""
         await asyncio.sleep(0)
 
+    async def submit_and_get_trace_id(self):
+        """Simulate async submission and return trace ID."""
+        await asyncio.sleep(0)
+        self._submitted_trace_id = "test-trace-id-12345"
+        return self._submitted_trace_id
+
     async def aclose(self):
         """Simulate async close."""
         await asyncio.sleep(0)
@@ -372,6 +379,110 @@ def handler(data, context):
     assert tracker.started[-1][2] is True  # is_evaluation flag
 
 
+def test_streaming_with_evaluation_id_collects_and_returns_complete_response(
+    patch_helpers,
+):
+    """Test that streaming with evaluation-id collects all chunks and returns complete response."""
+    tracker = patch_helpers
+
+    @entrypoint
+    async def handler(data):
+        yield "hello"
+        yield " "
+        yield "world"
+
+    fastapi_app = globals()["fastapi_app"]
+    with TestClient(fastapi_app) as client:
+        # With evaluation-id header, response should NOT be streamed
+        r = client.post(
+            "/run", json={"test": 1}, headers={"evaluation-id": "eval-123"}
+        )
+        assert r.status_code == 200
+        # Response should be the complete collected output
+        assert r.json() == "hello world"
+        # Trace ID should be in response headers
+        assert r.headers.get("X-Gradient-Trace-Id") == "test-trace-id-12345"
+
+    # Check that is_evaluation was passed correctly
+    assert tracker.started
+    assert tracker.started[-1][2] is True  # is_evaluation flag
+    # Tracker should have the collected output
+    assert tracker._req.get("outputs") == "hello world"
+    # submit_and_get_trace_id should have been called
+    assert tracker._submitted_trace_id == "test-trace-id-12345"
+
+
+def test_streaming_without_evaluation_id_streams_normally(patch_helpers):
+    """Test that streaming without evaluation-id continues to stream normally."""
+    tracker = patch_helpers
+
+    @entrypoint
+    async def handler(data):
+        yield "hello"
+        yield " "
+        yield "world"
+
+    fastapi_app = globals()["fastapi_app"]
+    with TestClient(fastapi_app) as client:
+        # Without evaluation-id header, response should be streamed
+        with client.stream("POST", "/run", json={"test": 1}) as resp:
+            assert resp.status_code == 200
+            # Read the full stream by iterating
+            body = "".join(chunk for chunk in resp.iter_text())
+            assert body == "hello world"
+
+    # Check that is_evaluation was passed as False
+    assert tracker.started
+    assert tracker.started[-1][2] is False  # is_evaluation flag
+    # submit_and_get_trace_id should NOT have been called (normal streaming)
+    assert tracker._submitted_trace_id is None
+
+
+def test_streaming_with_evaluation_id_handles_dict_chunks(patch_helpers):
+    """Test that streaming with evaluation-id properly handles dict chunks."""
+    tracker = patch_helpers
+
+    @entrypoint
+    async def handler(data):
+        yield {"type": "start"}
+        yield {"type": "data", "value": 42}
+        yield {"type": "end"}
+
+    fastapi_app = globals()["fastapi_app"]
+    with TestClient(fastapi_app) as client:
+        r = client.post(
+            "/run", json={"test": 1}, headers={"evaluation-id": "eval-123"}
+        )
+        assert r.status_code == 200
+        # Dict chunks should be JSON serialized and concatenated
+        result = r.json()
+        assert '{"type": "start"}' in result
+        assert '{"type": "data", "value": 42}' in result
+        assert '{"type": "end"}' in result
+        # Trace ID should be in response headers
+        assert r.headers.get("X-Gradient-Trace-Id") == "test-trace-id-12345"
+
+
+def test_streaming_with_evaluation_id_skips_none_chunks(patch_helpers):
+    """Test that streaming with evaluation-id properly skips None chunks."""
+    tracker = patch_helpers
+
+    @entrypoint
+    async def handler(data):
+        yield "a"
+        yield None  # Should be skipped
+        yield "b"
+
+    fastapi_app = globals()["fastapi_app"]
+    with TestClient(fastapi_app) as client:
+        r = client.post(
+            "/run", json={"test": 1}, headers={"evaluation-id": "eval-123"}
+        )
+        assert r.status_code == 200
+        assert r.json() == "ab"  # None skipped
+        assert r.headers.get("X-Gradient-Trace-Id") == "test-trace-id-12345"
+
+
 def test_shutdown_event_calls_tracker_aclose(patch_helpers):
     """Test that shutdown event calls tracker aclose."""
     tracker = patch_helpers
@@ -414,4 +525,4 @@ def handler(data, context):
     assert calls["host"] == "127.0.0.1"
     assert calls["port"] == 9999
     assert calls["kwargs"]["reload"] is True
-    assert calls["kwargs"]["log_level"] == "debug"
+    assert calls["kwargs"]["log_level"] == "debug"
\ No newline at end of file