Add Anthropic to OpenAI format transformation for spend logs

Fixes #22195.

Transform Anthropic API requests to OpenAI-compatible format when logging
to spend logs. This ensures consistent format across different providers.

- Add _transform_anthropic_request_to_openai_format() function
- Convert Anthropic's system field to system message in messages array
- Transform Anthropic's tool input_schema to OpenAI function parameters
- Apply transformation for requests to /messages endpoint

litellm/proxy/spend_tracking/spend_tracking_utils.py

@@ -744,6 +744,45 @@ def _convert_to_json_serializable_dict(
             visited.remove(obj_id)
 
 
+def _transform_anthropic_request_to_openai_format(request_body: dict) -> dict:
+    """
+    Transform Anthropic API request format to OpenAI-compatible format.
+    Anthropic uses a different format for system messages and tool definitions:
+    - System messages: separate 'system' field -> converted to system message in messages array
+    - Tools: Anthropic's input_schema -> OpenAI's function parameters
+    Args:
+        request_body: The request body from Anthropic /messages endpoint
+    Returns:
+        Transformed request body in OpenAI-compatible format
+    """
+    # Transform system message if present
+    request_body = dict(request_body)
+    system_content = request_body.pop("system", None)
+    if system_content:
+        request_body["messages"] = [
+            {"role": "system", "content": system_content}
+        ] + request_body.get("messages", [])
+
+    # Transform tools if present
+    if "tools" in request_body and request_body["tools"]:
+        request_body["tools"] = [
+            {
+                "type": "function",
+                "function": {
+                    "name": t["name"],
+                    "description": t.get("description", ""),
+                    "parameters": t.get(
+                        "input_schema", {}
+                    ),  # Anthropic-specific tools (e.g., computer_20241022) lack input_schema
+                },
+            }
+            for t in request_body.get("tools", [])
+            if "name" in t  # Valid tools should have a name
+        ]
+
+    return request_body
+
+
 def _get_proxy_server_request_for_spend_logs_payload(
     metadata: dict,
     litellm_params: dict,
@@ -787,6 +826,13 @@ def _get_proxy_server_request_for_spend_logs_payload(
                     _request_body = _convert_to_json_serializable_dict(_request_body)
                     perform_redaction(model_call_details=_request_body, result=None)
 
+            # Transform Anthropic format to OpenAI format if this is an Anthropic request
+            _request_uri = _proxy_server_request.get("url") or ""
+            if "/v1/messages" in _request_uri:
+                _request_body = _transform_anthropic_request_to_openai_format(
+                    _request_body
+                )
+
             _request_body = _sanitize_request_body_for_spend_logs_payload(_request_body)
             _request_body_json_str = json.dumps(_request_body, default=str)
             if LITELLM_TRUNCATED_PAYLOAD_FIELD in _request_body_json_str: