diff --git a/tests/test_litellm/llms/anthropic/experimental_pass_through/messages/test_anthropic_messages_streaming_success_logging.py b/tests/test_litellm/llms/anthropic/experimental_pass_through/messages/test_anthropic_messages_streaming_success_logging.py
new file mode 100644
index 00000000000..88bb09c99fd
--- /dev/null
+++ b/tests/test_litellm/llms/anthropic/experimental_pass_through/messages/test_anthropic_messages_streaming_success_logging.py
@@ -0,0 +1,192 @@
+import asyncio
+import json
+import threading
+from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
+from typing import Any, Dict, List, Optional, Tuple
+
+import pytest
+
+import litellm
+from litellm.integrations.custom_logger import CustomLogger
+
+MODEL = "gpt-4o-mini"
+PROMPT_TOKENS = 5
+COMPLETION_TOKENS = 2
+
+
+def _chat_completion_chunks() -> Tuple[Dict[str, Any], ...]:
+    def chunk(delta: Dict[str, Any], finish_reason: Optional[str] = None) -> Dict[str, Any]:
+        return {
+            "id": "chatcmpl-1",
+            "object": "chat.completion.chunk",
+            "created": 1,
+            "model": MODEL,
+            "choices": [{"index": 0, "delta": delta, "finish_reason": finish_reason}],
+        }
+
+    return (
+        chunk({"role": "assistant", "content": ""}),
+        chunk({"content": "hello"}),
+        chunk({}, finish_reason="stop"),
+        {
+            "id": "chatcmpl-1",
+            "object": "chat.completion.chunk",
+            "created": 1,
+            "model": MODEL,
+            "choices": [],
+            "usage": {
+                "prompt_tokens": PROMPT_TOKENS,
+                "completion_tokens": COMPLETION_TOKENS,
+                "total_tokens": PROMPT_TOKENS + COMPLETION_TOKENS,
+            },
+        },
+    )
+
+
+def _responses_api_chunks() -> Tuple[Dict[str, Any], ...]:
+    in_progress = {
+        "id": "resp_1",
+        "object": "response",
+        "created_at": 1,
+        "model": MODEL,
+        "status": "in_progress",
+        "output": [],
+        "parallel_tool_calls": False,
+        "tool_choice": "auto",
+        "tools": [],
+    }
+    message_item = {
+        "id": "msg_1",
+        "type": "message",
+        "role": "assistant",
+        "status": "completed",
+        "content": [{"type": "output_text", "text": "hello", "annotations": []}],
+    }
+    completed = {
+        **in_progress,
+        "status": "completed",
+        "output": [message_item],
+        "usage": {
+            "input_tokens": PROMPT_TOKENS,
+            "output_tokens": COMPLETION_TOKENS,
+            "total_tokens": PROMPT_TOKENS + COMPLETION_TOKENS,
+        },
+    }
+    return (
+        {"type": "response.created", "response": in_progress, "sequence_number": 0},
+        {
+            "type": "response.output_item.added",
+            "output_index": 0,
+            "sequence_number": 1,
+            "item": {**message_item, "status": "in_progress", "content": []},
+        },
+        {
+            "type": "response.output_text.delta",
+            "item_id": "msg_1",
+            "output_index": 0,
+            "content_index": 0,
+            "delta": "hello",
+            "sequence_number": 2,
+        },
+        {
+            "type": "response.output_item.done",
+            "output_index": 0,
+            "item": message_item,
+            "sequence_number": 3,
+        },
+        {"type": "response.completed", "response": completed, "sequence_number": 4},
+    )
+
+
+class _MockOpenAIHandler(BaseHTTPRequestHandler):
+    protocol_version = "HTTP/1.1"
+
+    def log_message(self, *args: Any) -> None:
+        pass
+
+    def do_POST(self) -> None:
+        content_length = int(self.headers.get("content-length", 0))
+        self.rfile.read(content_length)
+
+        chunks = _responses_api_chunks() if self.path.endswith("/responses") else _chat_completion_chunks()
+
+        self.send_response(200)
+        self.send_header("content-type", "text/event-stream")
+        self.send_header("transfer-encoding", "chunked")
+        self.end_headers()
+        for chunk in chunks:
+            self._write_chunk(f"data: {json.dumps(chunk)}\n\n".encode())
+        self._write_chunk(b"data: [DONE]\n\n")
+        self._write_chunk(b"")
+
+    def _write_chunk(self, body: bytes) -> None:
+        self.wfile.write(f"{len(body):X}\r\n".encode() + body + b"\r\n")
+        self.wfile.flush()
+
+
+class _RecordingLogger(CustomLogger):
+    def __init__(self) -> None:
+        super().__init__()
+        self.payloads: List[Dict[str, Any]] = []
+
+    async def async_log_success_event(self, kwargs, response_obj, start_time, end_time) -> None:
+        standard_logging_object = kwargs.get("standard_logging_object")
+        if standard_logging_object is not None:
+            self.payloads.append(standard_logging_object)
+
+
+async def _wait_for_payload(logger: _RecordingLogger) -> Dict[str, Any]:
+    for _ in range(100):
+        if logger.payloads:
+            return logger.payloads[0]
+        await asyncio.sleep(0.05)
+    raise AssertionError("no success logging callback fired for the streamed /v1/messages request")
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("use_chat_completions_bridge", [True, False])
+async def test_streaming_anthropic_messages_to_openai_backend_logs_usage(
+    monkeypatch: pytest.MonkeyPatch, use_chat_completions_bridge: bool
+) -> None:
+    """
+    Streaming /v1/messages against an ``openai/`` deployment must emit a success
+    logging callback with real usage, on both bridges: the chat-completions
+    adapter (``AnthropicStreamWrapper``) and the Responses API adapter
+    (``AnthropicResponsesStreamWrapper``). Regression test for #35124, where the
+    Responses bridge streamed a correct SSE body but never logged, so the
+    request was billed by the provider and recorded with 0 tokens / $0 cost.
+    """
+    monkeypatch.setattr(
+        litellm,
+        "use_chat_completions_url_for_anthropic_messages",
+        use_chat_completions_bridge,
+    )
+    logger = _RecordingLogger()
+    monkeypatch.setattr(litellm, "callbacks", [logger])
+    monkeypatch.setattr(litellm, "success_callback", [])
+    monkeypatch.setattr(litellm, "_async_success_callback", [])
+
+    server = ThreadingHTTPServer(("127.0.0.1", 0), _MockOpenAIHandler)
+    threading.Thread(target=server.serve_forever, daemon=True).start()
+    try:
+        stream = await litellm.anthropic.messages.acreate(
+            model=f"openai/{MODEL}",
+            api_base=f"http://127.0.0.1:{server.server_port}",
+            api_key="test",
+            messages=[{"role": "user", "content": "hi"}],
+            max_tokens=100,
+            stream=True,
+        )
+        events = [chunk async for chunk in stream]
+        assert b"event: message_stop" in b"".join(events)
+
+        payload = await _wait_for_payload(logger)
+    finally:
+        server.shutdown()
+        server.server_close()
+
+    assert payload["call_type"] == "anthropic_messages"
+    assert payload["prompt_tokens"] == PROMPT_TOKENS
+    assert payload["completion_tokens"] == COMPLETION_TOKENS
+    assert payload["total_tokens"] == PROMPT_TOKENS + COMPLETION_TOKENS
+    assert payload["response_cost"] > 0