fix(proxy): remove per-chunk debug log in async_data_generator

Remove verbose_proxy_logger.debug that formatted every streaming chunk,
which triggered expensive Pydantic serialization on the hot path.

litellm/litellm_core_utils/streaming_handler.py

@@ -1929,9 +1929,10 @@ class CustomStreamWrapper:
                         hasattr(processed_chunk, "usage")
                         and getattr(processed_chunk, "usage", None) is not None
                     ):
-                        # Flag for proxy to exclude usage during serialization
-                        # instead of expensive model_dump() + reconstruct round-trip
-                        processed_chunk._usage_stripped = True  # type: ignore
+                        # Set usage to None so model_dump_json(exclude_none=True)
+                        # drops it. The original usage is already preserved in
+                        # self.chunks (appended above) for calculate_total_usage().
+                        processed_chunk.usage = None  # type: ignore
                         is_empty = is_model_response_stream_empty(
                             model_response=cast(ModelResponseStream, processed_chunk)
                         )

litellm/proxy/proxy_server.py

@@ -5094,14 +5094,7 @@ async def async_data_generator(
             )
 
             if isinstance(chunk, BaseModel):
-                if getattr(chunk, "_usage_stripped", False):
-                    chunk = chunk.model_dump_json(
-                        exclude_none=True, exclude_unset=True, exclude={"usage"}  # type: ignore
-                    )
-                else:
-                    chunk = chunk.model_dump_json(
-                        exclude_none=True, exclude_unset=True
-                    )
+                chunk = chunk.model_dump_json(exclude_none=True, exclude_unset=True)
             elif isinstance(chunk, str) and chunk.startswith("data: "):
                 error_message = chunk
                 break

tests/test_litellm/proxy/middleware/test_prometheus_auth_middleware_asgi.py

@@ -0,0 +1,24 @@
+"""
+Tests that PrometheusAuthMiddleware is a pure ASGI middleware (not BaseHTTPMiddleware).
+
+BaseHTTPMiddleware wraps streaming responses with receive_or_disconnect per chunk,
+which blocks the event loop and causes severe throughput degradation.
+"""
+from starlette.middleware.base import BaseHTTPMiddleware
+
+from litellm.proxy.middleware.prometheus_auth_middleware import PrometheusAuthMiddleware
+
+
+def test_is_not_base_http_middleware():
+    """PrometheusAuthMiddleware must NOT inherit from BaseHTTPMiddleware."""
+    assert not issubclass(PrometheusAuthMiddleware, BaseHTTPMiddleware), (
+        "PrometheusAuthMiddleware should be a pure ASGI middleware, not BaseHTTPMiddleware. "
+        "BaseHTTPMiddleware causes severe streaming performance degradation."
+    )
+
+
+def test_has_asgi_call_protocol():
+    """PrometheusAuthMiddleware must implement the ASGI __call__ protocol."""
+    assert "__call__" in PrometheusAuthMiddleware.__dict__, (
+        "PrometheusAuthMiddleware must define __call__(self, scope, receive, send)"
+    )