fix(proxy): recognize crlf sse frame boundaries in passthrough reassembly

litellm/proxy/common_request_processing.py

@@ -3066,7 +3066,7 @@ class ProxyBaseLLMRequestProcessing:
             elif isinstance(chunk, (bytes, bytearray)):
                 try:
                     s: Final = chunk.decode("utf-8")
-                    if s.endswith("\n\n"):
+                    if s.endswith(("\n\n", "\r\n\r\n")):
                         maybe_mod = ProxyBaseLLMRequestProcessing._inject_cost_into_sse_frame_str(s, model_name)
                         if maybe_mod is not None:
                             return maybe_mod.encode("utf-8")

litellm/proxy/pass_through_endpoints/streaming_handler.py

@@ -141,10 +141,12 @@ class PassThroughStreamingHandler:
 
     @staticmethod
     def _split_complete_sse_frames(pending: bytes) -> tuple[bytes, bytes]:
-        frame_boundary: Final = pending.rfind(b"\n\n")
-        if frame_boundary == -1:
+        lf_boundary_end: Final = pending.rfind(b"\n\n") + 2
+        crlf_boundary_end: Final = pending.rfind(b"\r\n\r\n") + 4
+        boundary_end: Final = max(lf_boundary_end if lf_boundary_end >= 2 else 0, crlf_boundary_end if crlf_boundary_end >= 4 else 0)
+        if boundary_end == 0:
             return b"", pending
-        return pending[: frame_boundary + 2], pending[frame_boundary + 2 :]
+        return pending[:boundary_end], pending[boundary_end:]
 
     @staticmethod
     async def _route_streaming_logging_to_handler(

tests/test_litellm/proxy/pass_through_endpoints/test_streaming_handler_interrupt.py

@@ -443,6 +443,24 @@ async def test_chunk_processor_injects_cost_into_usage_frame_fragmented_across_c
     assert reassembled.endswith("data: [DONE]\n\n")
 
 
+@pytest.mark.asyncio
+async def test_chunk_processor_streams_crlf_delimited_frames_live_and_injects_cost(monkeypatch):
+    """Regression: CRLF-delimited SSE frames must flow as they complete instead of
+    buffering until EOF, and the usage frame must still get cost injected."""
+    monkeypatch.setattr(litellm, "include_cost_in_streaming_usage", True)
+    chunks = [chunk.replace(b"\n\n", b"\r\n\r\n") for chunk in _openai_passthrough_stream_chunks()]
+
+    received = await _collect_openai_passthrough_chunks(chunks, EndpointType.OPENAI)
+
+    assert len(received) == len(chunks)
+    assert received[0] == chunks[0]
+    reassembled = b"".join(received).decode("utf-8")
+    usage_lines = [ln for ln in reassembled.replace("\r\n", "\n").split("\n") if '"total_tokens"' in ln]
+    assert len(usage_lines) == 1
+    final_payload = json.loads(usage_lines[0].split("data:", 1)[1].strip())
+    assert final_payload["usage"]["cost"] > 0
+
+
 @pytest.mark.asyncio
 async def test_chunk_processor_flag_off_leaves_openai_passthrough_stream_byte_identical(monkeypatch):
     monkeypatch.setattr(litellm, "include_cost_in_streaming_usage", False)