diff --git a/tests/test_litellm/llms/sap/chat/test_sap_stream_chunk_validation.py b/tests/test_litellm/llms/sap/chat/test_sap_stream_chunk_validation.py
new file mode 100644
index 00000000000..018cd89e195
--- /dev/null
+++ b/tests/test_litellm/llms/sap/chat/test_sap_stream_chunk_validation.py
@@ -0,0 +1,104 @@
+"""
+Tests for SAP orchestration stream chunk normalization (_StreamParser._validate_chunk)
+and the descriptive error raised when no orchestration deployment exists.
+
+Regression tests for:
+- TypeError: 'MockValSer' object is not an instance of 'SchemaSerializer'
+  raised from nested model_dump() when the raw openai-SDK usage object
+  (a deferred-build pydantic model) was attached to ModelResponseStream.
+- IndexError: list index out of range raised from deployment_url when the
+  configured resource group contains no orchestration deployment.
+"""
+
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from litellm.llms.sap.chat.handler import GenAIHubOrchestrationError, _StreamParser
+from litellm.types.utils import ModelResponseStream, Usage
+
+
+def _final_chunk_payload() -> dict:
+    """OpenAI-shaped final chunk as sent by the SAP orchestration service:
+    every choice carries an empty `logprobs` ({}) and the last chunk carries usage."""
+    return {
+        "id": "chatcmpl-sap-final",
+        "object": "chat.completion.chunk",
+        "created": 1761319270,
+        "model": "anthropic--claude-4.7-opus",
+        "choices": [
+            {
+                "index": 0,
+                "delta": {},
+                "logprobs": {},
+                "finish_reason": "tool_calls",
+            }
+        ],
+        "usage": {
+            "completion_tokens": 206,
+            "prompt_tokens": 62322,
+            "total_tokens": 62528,
+        },
+    }
+
+
+def test_validate_chunk_drops_empty_logprobs():
+    chunk = _StreamParser._validate_chunk(_final_chunk_payload())
+    assert chunk.choices[0].logprobs is None
+
+
+def test_validate_chunk_preserves_real_logprobs():
+    payload = _final_chunk_payload()
+    payload["choices"][0]["logprobs"] = {
+        "content": [{"token": "Hello", "logprob": -0.1, "bytes": None, "top_logprobs": []}]
+    }
+    chunk = _StreamParser._validate_chunk(payload)
+    assert chunk.choices[0].logprobs is not None
+    assert chunk.choices[0].logprobs.content[0].token == "Hello"
+
+
+def test_validate_chunk_converts_usage_to_litellm_usage():
+    chunk = _StreamParser._validate_chunk(_final_chunk_payload())
+    assert isinstance(chunk.usage, Usage)
+    assert chunk.usage.completion_tokens == 206
+    assert chunk.usage.prompt_tokens == 62322
+    assert chunk.usage.total_tokens == 62528
+
+
+def test_validate_chunk_without_usage_keeps_none():
+    payload = _final_chunk_payload()
+    del payload["usage"]
+    chunk = _StreamParser._validate_chunk(payload)
+    assert chunk.usage is None
+
+
+def test_validated_usage_survives_nested_model_dump():
+    """The original crash: the raw openai-SDK usage object attached to a
+    ModelResponseStream made model_dump() raise
+    "TypeError: 'MockValSer' object is not an instance of 'SchemaSerializer'"."""
+    chunk = _StreamParser._validate_chunk(_final_chunk_payload())
+
+    model_response = ModelResponseStream()
+    setattr(model_response, "usage", chunk.usage)
+
+    dumped = model_response.model_dump()  # must not raise
+    assert dumped["usage"]["total_tokens"] == 62528
+
+
+def test_deployment_url_raises_404_when_no_orchestration_deployment():
+    from litellm.llms.sap.chat.transformation import GenAIHubOrchestrationConfig
+
+    config = GenAIHubOrchestrationConfig()
+    config.token_creator = lambda: "Bearer FAKE_TOKEN"
+    config._base_url = "https://api.ai.mock-sap.com/v2"
+    config._resource_group = "fake-group"
+
+    mock_client = MagicMock()
+    mock_client.get.return_value.json.return_value = {"resources": []}
+
+    with patch("litellm.module_level_client", mock_client):
+        with pytest.raises(GenAIHubOrchestrationError) as exc_info:
+            _ = config.deployment_url
+
+    assert exc_info.value.status_code == 404
+    assert "fake-group" in exc_info.value.message