diff --git a/litellm/completion_extras/litellm_responses_transformation/transformation.py b/litellm/completion_extras/litellm_responses_transformation/transformation.py
index da3b9184edb..221ca7e2a16 100644
--- a/litellm/completion_extras/litellm_responses_transformation/transformation.py
+++ b/litellm/completion_extras/litellm_responses_transformation/transformation.py
@@ -583,6 +583,126 @@ class LiteLLMResponsesTransformationHandler(CompletionTransformationBridge):
 
         return choices
 
+    @classmethod
+    def _recover_output_items_from_raw_sse(
+        cls, raw_sse: Optional[str]
+    ) -> List[Dict[str, Any]]:
+        if not raw_sse or not isinstance(raw_sse, str):
+            return []
+
+        from litellm.utils import CustomStreamWrapper
+
+        recovered_output_items: Dict[int, Dict[str, Any]] = {}
+        recovered_text_only_items: Dict[int, Dict[str, Any]] = {}
+
+        for chunk in raw_sse.splitlines():
+            stripped_chunk = (
+                CustomStreamWrapper._strip_sse_data_from_chunk(chunk.strip()) or ""
+            ).strip()
+            if (
+                not stripped_chunk
+                or stripped_chunk == "[DONE]"
+                or stripped_chunk.startswith("event:")
+            ):
+                continue
+
+            try:
+                parsed_chunk = json.loads(stripped_chunk)
+            except json.JSONDecodeError:
+                continue
+
+            if not isinstance(parsed_chunk, dict):
+                continue
+
+            event_type = parsed_chunk.get("type")
+            if event_type == ResponsesAPIStreamEvents.RESPONSE_COMPLETED:
+                response_payload = parsed_chunk.get("response")
+                if isinstance(response_payload, dict):
+                    response_output = response_payload.get("output")
+                    if isinstance(response_output, list) and len(response_output) > 0:
+                        return cast(List[Dict[str, Any]], response_output)
+                continue
+
+            if event_type == ResponsesAPIStreamEvents.OUTPUT_ITEM_DONE:
+                item = parsed_chunk.get("item")
+                if not isinstance(item, dict):
+                    continue
+                try:
+                    output_index = int(parsed_chunk.get("output_index"))
+                except (TypeError, ValueError):
+                    output_index = len(recovered_output_items)
+                recovered_output_items[output_index] = item
+                continue
+
+            if event_type == ResponsesAPIStreamEvents.OUTPUT_TEXT_DONE:
+                text = parsed_chunk.get("text")
+                if not isinstance(text, str):
+                    continue
+
+                try:
+                    output_index = int(parsed_chunk.get("output_index"))
+                except (TypeError, ValueError):
+                    output_index = len(recovered_text_only_items)
+
+                item = recovered_output_items.get(
+                    output_index
+                ) or recovered_text_only_items.get(output_index)
+                if item is None:
+                    item = {
+                        "type": "message",
+                        "id": parsed_chunk.get("item_id") or f"msg_{output_index}",
+                        "role": "assistant",
+                        "status": "completed",
+                        "content": [],
+                    }
+                    recovered_text_only_items[output_index] = item
+
+                content = item.setdefault("content", [])
+                if not isinstance(content, list):
+                    continue
+
+                try:
+                    content_index = int(parsed_chunk.get("content_index"))
+                except (TypeError, ValueError):
+                    content_index = len(content)
+
+                while len(content) <= content_index:
+                    content.append(
+                        {
+                            "type": "output_text",
+                            "text": "",
+                            "annotations": [],
+                        }
+                    )
+
+                content_item = content[content_index]
+                if not isinstance(content_item, dict):
+                    content_item = {}
+                    content[content_index] = content_item
+
+                content_item["type"] = "output_text"
+                content_item["text"] = text
+                if parsed_chunk.get("annotations") is not None:
+                    content_item["annotations"] = parsed_chunk["annotations"]
+                else:
+                    content_item.setdefault("annotations", [])
+
+        if recovered_output_items:
+            return [item for _, item in sorted(recovered_output_items.items())]
+
+        if recovered_text_only_items:
+            return [item for _, item in sorted(recovered_text_only_items.items())]
+
+        return []
+
+    @classmethod
+    def _recover_output_items_from_logging(
+        cls, logging_obj: "LiteLLMLoggingObj"
+    ) -> List[Dict[str, Any]]:
+        model_call_details = getattr(logging_obj, "model_call_details", {}) or {}
+        original_response = model_call_details.get("original_response")
+        return cls._recover_output_items_from_raw_sse(original_response)
+
     def transform_response(  # noqa: PLR0915
         self,
         model: str,
@@ -607,9 +727,21 @@ class LiteLLMResponsesTransformationHandler(CompletionTransformationBridge):
         if raw_response.error is not None:
             raise ValueError(f"Error in response: {raw_response.error}")
 
+        output_items = raw_response.output
+        if len(output_items) == 0:
+            recovered_output_items = self._recover_output_items_from_logging(
+                logging_obj
+            )
+            if recovered_output_items:
+                output_items = recovered_output_items
+                verbose_logger.warning(
+                    "Recovered empty Responses API output from raw SSE for model=%s",
+                    model,
+                )
+
         # Convert response output to choices using the static helper
         choices = self._convert_response_output_to_choices(
-            output_items=raw_response.output,
+            output_items=output_items,
             handle_raw_dict_callback=self._handle_raw_dict_response_item,
         )
 
@@ -623,7 +755,7 @@ class LiteLLMResponsesTransformationHandler(CompletionTransformationBridge):
                 )
             else:
                 raise ValueError(
-                    f"Unknown items in responses API response: {raw_response.output}"
+                    f"Unknown items in responses API response: {output_items}"
                 )
 
         setattr(model_response, "choices", choices)
diff --git a/litellm/llms/chatgpt/responses/transformation.py b/litellm/llms/chatgpt/responses/transformation.py
index 66acd933416..4874f08d05e 100644
--- a/litellm/llms/chatgpt/responses/transformation.py
+++ b/litellm/llms/chatgpt/responses/transformation.py
@@ -1,5 +1,5 @@
 import json
-from typing import Any, Optional
+from typing import Any, Dict, Optional
 
 from litellm.constants import STREAM_SSE_DONE_STRING
 from litellm.exceptions import AuthenticationError
@@ -134,6 +134,7 @@ class ChatGPTResponsesAPIConfig(OpenAIResponsesAPIConfig):
 
         completed_response = None
         error_message = None
+        streamed_output_items: Dict[int, dict] = {}
         for chunk in body_text.splitlines():
             stripped_chunk = CustomStreamWrapper._strip_sse_data_from_chunk(chunk)
             if not stripped_chunk:
@@ -150,10 +151,24 @@ class ChatGPTResponsesAPIConfig(OpenAIResponsesAPIConfig):
             if not isinstance(parsed_chunk, dict):
                 continue
             event_type = parsed_chunk.get("type")
+            if event_type == ResponsesAPIStreamEvents.OUTPUT_ITEM_DONE:
+                item = parsed_chunk.get("item")
+                output_index = parsed_chunk.get("output_index")
+                if isinstance(item, dict):
+                    try:
+                        index = int(output_index)
+                    except (TypeError, ValueError):
+                        index = len(streamed_output_items)
+                    streamed_output_items[index] = item
+                continue
             if event_type == ResponsesAPIStreamEvents.RESPONSE_COMPLETED:
                 response_payload = parsed_chunk.get("response")
                 if isinstance(response_payload, dict):
                     response_payload = dict(response_payload)
+                    if not response_payload.get("output") and streamed_output_items:
+                        response_payload["output"] = [
+                            item for _, item in sorted(streamed_output_items.items())
+                        ]
                     if "created_at" in response_payload:
                         response_payload["created_at"] = _safe_convert_created_field(
                             response_payload["created_at"]
diff --git a/litellm/router.py b/litellm/router.py
index 7512ee387dc..749f5fc762c 100644
--- a/litellm/router.py
+++ b/litellm/router.py
@@ -7076,6 +7076,18 @@ class Router:
             _shared_model_info = {
                 k: v for k, v in _model_info.items() if k not in _custom_pricing_fields
             }
+            _existing_shared_mode = (
+                cast(Optional[dict], litellm.model_cost.get(_model_name, {})) or {}
+            ).get("mode")
+            if (
+                _existing_shared_mode is not None
+                and _shared_model_info.get("mode") != _existing_shared_mode
+            ):
+                # Keep the built-in bridge mode stable for shared backend keys.
+                # Multiple aliases can point at the same provider/model backend,
+                # but their deployment-level overrides should not downgrade the
+                # backend from responses -> chat via last-write-wins registration.
+                _shared_model_info.pop("mode", None)
             litellm.register_model(
                 model_cost={
                     _model_name: _shared_model_info,
diff --git a/tests/test_litellm/completion_extras/litellm_responses_transformation/test_completion_extras_litellm_responses_transformation_transformation.py b/tests/test_litellm/completion_extras/litellm_responses_transformation/test_completion_extras_litellm_responses_transformation_transformation.py
index e40543e01a0..2c223a43a16 100644
--- a/tests/test_litellm/completion_extras/litellm_responses_transformation/test_completion_extras_litellm_responses_transformation_transformation.py
+++ b/tests/test_litellm/completion_extras/litellm_responses_transformation/test_completion_extras_litellm_responses_transformation_transformation.py
@@ -508,6 +508,136 @@ and I learn to carry this small calm home."""
     print("✓ transform_response correctly handled reasoning items and output messages")
 
 
+def _make_empty_responses_api_response(model: str = "gpt-5.4"):
+    from litellm.types.llms.openai import ResponseAPIUsage, ResponsesAPIResponse
+
+    return ResponsesAPIResponse(
+        id="resp_from_stream",
+        created_at=1760144904,
+        error=None,
+        incomplete_details=None,
+        instructions=None,
+        metadata={},
+        model=model,
+        object="response",
+        output=[],
+        parallel_tool_calls=True,
+        temperature=1.0,
+        tool_choice="auto",
+        tools=[],
+        top_p=1.0,
+        max_output_tokens=None,
+        previous_response_id=None,
+        reasoning={"effort": "low", "summary": "detailed"},
+        status="completed",
+        text={"format": {"type": "text"}, "verbosity": "medium"},
+        truncation="disabled",
+        usage=ResponseAPIUsage(
+            input_tokens=1,
+            input_tokens_details=None,
+            output_tokens=1,
+            output_tokens_details=None,
+            total_tokens=2,
+            cost=None,
+        ),
+        user=None,
+        store=True,
+        background=False,
+        billing={"payer": "developer"},
+        max_tool_calls=None,
+        prompt_cache_key=None,
+        safety_identifier=None,
+        service_tier="default",
+        top_logprobs=0,
+    )
+
+
+def _make_empty_model_response():
+    from litellm.types.utils import ModelResponse, Usage
+
+    return ModelResponse(
+        id="chatcmpl-test-recovered",
+        created=1760144904,
+        model=None,
+        object="chat.completion",
+        system_fingerprint=None,
+        choices=[],
+        usage=Usage(completion_tokens=0, prompt_tokens=0, total_tokens=0),
+    )
+
+
+def test_transform_response_recovers_empty_output_from_raw_sse():
+    from litellm.completion_extras.litellm_responses_transformation.transformation import (
+        LiteLLMResponsesTransformationHandler,
+    )
+
+    handler = LiteLLMResponsesTransformationHandler()
+    raw_sse = "\n".join(
+        [
+            'data: {"type":"response.output_text.done","output_index":0,"content_index":0,"item_id":"msg_from_stream","text":"Recovered from SSE"}',
+            'data: {"type":"response.completed","response":{"id":"resp_from_stream","object":"response","created_at":1760144904,"status":"completed","model":"gpt-5.4","output":[]}}',
+            "data: [DONE]",
+            "",
+        ]
+    )
+
+    raw_response = _make_empty_responses_api_response()
+    model_response = _make_empty_model_response()
+    logging_obj = Mock()
+    logging_obj.model_call_details = {"original_response": raw_sse}
+
+    result = handler.transform_response(
+        model="gpt-5.4",
+        raw_response=raw_response,
+        model_response=model_response,
+        logging_obj=logging_obj,
+        request_data={"model": "gpt-5.4"},
+        messages=[{"role": "user", "content": "Reply with exactly: ok"}],
+        optional_params={},
+        litellm_params={},
+        encoding=Mock(),
+    )
+
+    assert len(result.choices) == 1
+    assert result.choices[0].message.content == "Recovered from SSE"
+
+
+def test_transform_response_recovers_output_item_done_from_raw_sse():
+    from litellm.completion_extras.litellm_responses_transformation.transformation import (
+        LiteLLMResponsesTransformationHandler,
+    )
+
+    handler = LiteLLMResponsesTransformationHandler()
+    raw_sse = "\n".join(
+        [
+            'data: {"type":"response.output_item.done","output_index":0,"item":{"type":"message","id":"msg_from_item","role":"assistant","status":"completed","content":[{"type":"output_text","text":"Recovered from output item","annotations":[]}]}}',
+            'data: {"type":"response.completed","response":{"id":"resp_from_stream","object":"response","created_at":1760144904,"status":"completed","model":"gpt-5.4","output":[]}}',
+            "data: [DONE]",
+            "",
+        ]
+    )
+
+    raw_response = _make_empty_responses_api_response()
+    model_response = _make_empty_model_response()
+    logging_obj = Mock()
+    logging_obj.model_call_details = {"original_response": raw_sse}
+
+    result = handler.transform_response(
+        model="gpt-5.4",
+        raw_response=raw_response,
+        model_response=model_response,
+        logging_obj=logging_obj,
+        request_data={"model": "gpt-5.4"},
+        messages=[{"role": "user", "content": "Reply with exactly: ok"}],
+        optional_params={},
+        litellm_params={},
+        encoding=Mock(),
+    )
+
+    assert len(result.choices) == 1
+    assert result.choices[0].message.content == "Recovered from output item"
+
+
 def test_convert_tools_to_responses_format():
     from litellm.completion_extras.litellm_responses_transformation.transformation import (
         LiteLLMResponsesTransformationHandler,
diff --git a/tests/test_litellm/llms/chatgpt/responses/test_chatgpt_responses_transformation.py b/tests/test_litellm/llms/chatgpt/responses/test_chatgpt_responses_transformation.py
index 2498946bb5c..692a7e257dc 100644
--- a/tests/test_litellm/llms/chatgpt/responses/test_chatgpt_responses_transformation.py
+++ b/tests/test_litellm/llms/chatgpt/responses/test_chatgpt_responses_transformation.py
@@ -14,6 +14,7 @@ import pytest
 
 sys.path.insert(0, os.path.abspath("../../../../.."))
 
+from litellm.llms.openai.common_utils import OpenAIError
 from litellm.types.router import GenericLiteLLMParams
 from litellm.types.utils import LlmProviders
 from litellm.utils import ProviderConfigManager
@@ -201,3 +202,74 @@ class TestChatGPTResponsesAPITransformation:
         )
 
         assert parsed.output_text == "Hello!"
+
+    @pytest.mark.parametrize(
+        ("model_name", "response_model"),
+        [
+            ("chatgpt/gpt-5.2-codex", "gpt-5.2-codex"),
+            ("chatgpt/gpt-5.3-codex", "gpt-5.3-codex"),
+        ],
+    )
+    def test_chatgpt_non_stream_sse_response_recovers_output_items(
+        self, model_name: str, response_model: str
+    ):
+        config = ChatGPTResponsesAPIConfig()
+        output_item = {
+            "type": "message",
+            "id": "msg_test",
+            "role": "assistant",
+            "status": "completed",
+            "content": [{"type": "output_text", "text": "Hello from output item"}],
+        }
+        sse_body = "\n".join(
+            [
+                f"data: {json.dumps({'type': 'response.output_item.done', 'output_index': 0, 'item': output_item})}",
+                f"data: {json.dumps({'type': 'response.completed', 'response': {'id': 'resp_test', 'object': 'response', 'created_at': 1700000000, 'status': 'completed', 'model': response_model, 'output': []}})}",
+                "data: [DONE]",
+                "",
+            ]
+        )
+        raw_response = httpx.Response(
+            200, headers={"content-type": "text/event-stream"}, text=sse_body
+        )
+        logging_obj = MagicMock()
+
+        parsed = config.transform_response_api_response(
+            model=model_name,
+            raw_response=raw_response,
+            logging_obj=logging_obj,
+        )
+
+        assert parsed.output == [output_item]
+        assert parsed.output_text == "Hello from output item"
+
+    @pytest.mark.parametrize(
+        ("model_name", "response_model"),
+        [
+            ("chatgpt/gpt-5.2-codex", "gpt-5.2-codex"),
+            ("chatgpt/gpt-5.3-codex", "gpt-5.3-codex"),
+        ],
+    )
+    def test_chatgpt_non_stream_sse_response_raises_without_completed_response(
+        self, model_name: str, response_model: str
+    ):
+        config = ChatGPTResponsesAPIConfig()
+        sse_body = "\n".join(
+            [
+                f"data: {json.dumps({'type': 'response.output_item.done', 'output_index': 0, 'item': {'type': 'message', 'role': 'assistant', 'content': [{'type': 'output_text', 'text': 'Hello'}]}})}",
+                f"data: {json.dumps({'type': 'response.failed', 'response': {'error': {'message': f'{response_model} failed'}}})}",
+                "data: [DONE]",
+                "",
+            ]
+        )
+        raw_response = httpx.Response(
+            500, headers={"content-type": "text/event-stream"}, text=sse_body
+        )
+        logging_obj = MagicMock()
+
+        with pytest.raises(OpenAIError, match=f"{response_model} failed"):
+            config.transform_response_api_response(
+                model=model_name,
+                raw_response=raw_response,
+                logging_obj=logging_obj,
+            )
diff --git a/tests/test_litellm/test_router_model_cost_isolation.py b/tests/test_litellm/test_router_model_cost_isolation.py
index 7a9d5acaa27..70582fee88f 100644
--- a/tests/test_litellm/test_router_model_cost_isolation.py
+++ b/tests/test_litellm/test_router_model_cost_isolation.py
@@ -266,3 +266,41 @@ def test_should_preserve_builtin_pricing_regardless_of_deployment_order():
         f"Order should not matter. Expected {builtin_output_cost}, "
         f"got {info_std_2['output_cost_per_token']}"
     )
+
+
+def test_should_preserve_shared_chatgpt_backend_mode_for_aliases():
+    backend_model = "chatgpt/gpt-5.4"
+    builtin_info = litellm.get_model_info(model=backend_model)
+    builtin_mode = builtin_info.get("mode")
+
+    assert builtin_mode == "responses"
+
+    Router(
+        model_list=[
+            {
+                "model_name": "chatgpt-alias-a",
+                "litellm_params": {
+                    "model": backend_model,
+                    "api_key": "fake-key-chatgpt-a",
+                },
+                "model_info": {
+                    "id": "chatgpt-alias-a-id",
+                },
+            },
+            {
+                "model_name": "chatgpt-alias-b",
+                "litellm_params": {
+                    "model": backend_model,
+                    "api_key": "fake-key-chatgpt-b",
+                },
+                "model_info": {
+                    "id": "chatgpt-alias-b-id",
+                    "mode": "chat",
+                },
+            },
+        ],
+    )
+
+    shared_info = litellm.model_cost.get(backend_model)
+    assert shared_info is not None
+    assert shared_info.get("mode") == "responses"