feat: Enable PROGRESSIVE_SSE_STREAMING feature by default

Related: google#3705

Co-authored-by: Xuan Yang <xygoogle@google.com>
PiperOrigin-RevId: 846793027

Author: xuanyang15

src/google/adk/features/_feature_registry.py

@@ -89,7 +89,7 @@ class FeatureConfig:
         FeatureStage.WIP, default_on=False
     ),
     FeatureName.PROGRESSIVE_SSE_STREAMING: FeatureConfig(
-        FeatureStage.WIP, default_on=False
+        FeatureStage.EXPERIMENTAL, default_on=True
     ),
     FeatureName.PUBSUB_TOOLSET: FeatureConfig(
         FeatureStage.EXPERIMENTAL, default_on=True

tests/unittests/flows/llm_flows/test_progressive_sse_streaming.py

@@ -26,14 +26,6 @@
 from google.adk.runners import InMemoryRunner
 from google.adk.utils.streaming_utils import StreamingResponseAggregator
 from google.genai import types
-import pytest
-
-
-@pytest.fixture(autouse=True)
-def reset_env(monkeypatch):
-  monkeypatch.setenv("ADK_ENABLE_PROGRESSIVE_SSE_STREAMING", "1")
-  yield
-  monkeypatch.delenv("ADK_ENABLE_PROGRESSIVE_SSE_STREAMING")
 
 
 def get_weather(location: str) -> dict[str, Any]:

tests/unittests/models/test_google_llm.py

@@ -1116,10 +1116,16 @@ async def mock_coro():
         )
     ]
 
-    # Should have only 1 response (no aggregated content generated)
-    assert len(responses) == 1
-    # Verify it's a function call, not text
+    # With progressive SSE streaming enabled by default, we get 2 responses:
+    # 1. Partial response with function call
+    # 2. Final aggregated response with function call
+    assert len(responses) == 2
+    # First response is partial
+    assert responses[0].partial is True
     assert responses[0].content.parts[0].function_call is not None
+    # Second response is the final aggregated response
+    assert responses[1].partial is False
+    assert responses[1].content.parts[0].function_call is not None
 
 
 @pytest.mark.asyncio
@@ -1194,37 +1200,33 @@ async def mock_coro():
         )
     ]
 
-    # Should have multiple responses:
+    # With progressive SSE streaming enabled, we get 4 responses:
     # 1. Partial text "First text"
-    # 2. Aggregated "First text" when function call interrupts
-    # 3. Function call
-    # 4. Partial text " second text"
-    # 5. Final aggregated " second text"
-    assert len(responses) == 5
+    # 2. Partial function call
+    # 3. Partial text " second text"
+    # 4. Final aggregated response with all parts (text + FC + text)
+    assert len(responses) == 4
 
     # First partial text
     assert responses[0].partial is True
     assert responses[0].content.parts[0].text == "First text"
 
-    # Aggregated first text (when function call interrupts)
-    assert responses[1].content.parts[0].text == "First text"
-    assert (
-        responses[1].partial is None
-    )  # Aggregated responses don't have partial flag
-
-    # Function call
-    assert responses[2].content.parts[0].function_call is not None
-    assert responses[2].content.parts[0].function_call.name == "test_func"
+    # Partial function call
+    assert responses[1].partial is True
+    assert responses[1].content.parts[0].function_call is not None
+    assert responses[1].content.parts[0].function_call.name == "test_func"
 
-    # Second partial text
-    assert responses[3].partial is True
-    assert responses[3].content.parts[0].text == " second text"
+    # Partial second text
+    assert responses[2].partial is True
+    assert responses[2].content.parts[0].text == " second text"
 
-    # Final aggregated text with error info
-    assert responses[4].content.parts[0].text == " second text"
-    assert (
-        responses[4].error_code is None
-    )  # STOP finish reason should have None error_code
+    # Final aggregated response with all parts
+    assert responses[3].partial is False
+    assert len(responses[3].content.parts) == 3
+    assert responses[3].content.parts[0].text == "First text"
+    assert responses[3].content.parts[1].function_call.name == "test_func"
+    assert responses[3].content.parts[2].text == " second text"
+    assert responses[3].error_code is None  # STOP finish reason
 
 
 @pytest.mark.asyncio
@@ -1376,28 +1378,27 @@ async def mock_coro():
         )
     ]
 
-    # Should properly separate thought and regular text across aggregations
-    assert len(responses) > 5  # Multiple partial + aggregated responses
+    # With progressive SSE streaming, we get 6 responses:
+    # 5 partial responses + 1 final aggregated response
+    assert len(responses) == 6
 
-    # Verify we get both thought and regular text parts in aggregated responses
-    aggregated_responses = [
-        r
-        for r in responses
-        if r.partial is None and r.content and len(r.content.parts) > 1
-    ]
-    assert (
-        len(aggregated_responses) > 0
-    )  # Should have at least one aggregated response with multiple parts
+    # All but the last should be partial
+    for i in range(5):
+      assert responses[i].partial is True
 
-    # Final aggregated response should have both thought and text
+    # Final aggregated response should have all parts
     final_response = responses[-1]
-    assert (
-        final_response.error_code is None
-    )  # STOP finish reason should have None error_code
-    assert len(final_response.content.parts) == 2  # thought part + text part
+    assert final_response.partial is False
+    assert final_response.error_code is None  # STOP finish reason
+    # Final response aggregates: thought + text + FC + thought + text
+    assert len(final_response.content.parts) == 5
     assert final_response.content.parts[0].thought is True
-    assert "More thinking..." in final_response.content.parts[0].text
-    assert final_response.content.parts[1].text == " and conclusion"
+    assert "Thinking..." in final_response.content.parts[0].text
+    assert final_response.content.parts[1].text == "Here's my answer"
+    assert final_response.content.parts[2].function_call.name == "lookup"
+    assert final_response.content.parts[3].thought is True
+    assert "More thinking..." in final_response.content.parts[3].text
+    assert final_response.content.parts[4].text == " and conclusion"
 
 
 @pytest.mark.asyncio
@@ -1491,44 +1492,23 @@ async def mock_coro():
         )
     ]
 
-    # Find the aggregated text responses (non-partial, text-only)
-    aggregated_text_responses = [
-        r
-        for r in responses
-        if (
-            r.partial is None
-            and r.content
-            and r.content.parts
-            and r.content.parts[0].text
-            and not r.content.parts[0].function_call
-        )
-    ]
-
-    # Should have two separate text aggregations: "First chunk" and "Second chunk"
-    assert len(aggregated_text_responses) >= 2
+    # With progressive SSE streaming, we get 6 responses:
+    # 5 partial responses + 1 final aggregated response
+    assert len(responses) == 6
 
-    # First aggregation should contain "First chunk"
-    first_aggregation = aggregated_text_responses[0]
-    assert first_aggregation.content.parts[0].text == "First chunk"
+    # All but the last should be partial
+    for i in range(5):
+      assert responses[i].partial is True
 
-    # Final aggregation should contain "Second chunk" and have error info
-    final_aggregation = aggregated_text_responses[-1]
-    assert final_aggregation.content.parts[0].text == "Second chunk"
-    assert (
-        final_aggregation.error_code is None
-    )  # STOP finish reason should have None error_code
-
-    # Verify the function call is preserved between aggregations
-    function_call_responses = [
-        r
-        for r in responses
-        if (r.content and r.content.parts and r.content.parts[0].function_call)
-    ]
-    assert len(function_call_responses) == 1
-    assert (
-        function_call_responses[0].content.parts[0].function_call.name
-        == "divide"
-    )
+    # Final response should be aggregated with all parts
+    final_response = responses[-1]
+    assert final_response.partial is False
+    assert final_response.error_code is None  # STOP finish reason
+    # Final response aggregates: text1 + text2 + FC + text3 + text4
+    assert len(final_response.content.parts) == 3
+    assert final_response.content.parts[0].text == "First chunk"
+    assert final_response.content.parts[1].function_call.name == "divide"
+    assert final_response.content.parts[2].text == "Second chunk"
 
 
 @pytest.mark.asyncio