fix: detect Anthropic-format tool_use content blocks in orphan detection

- Update _is_orphaned_tool_result to check for tool_use content blocks
- Add tool_result to ValidUserMessageContentTypes
- Add tests for Anthropic-format tool content handling

Fixes #25669

Made-with: Cursor

litellm/litellm_core_utils/prompt_templates/factory.py

@@ -2218,6 +2218,7 @@ def _is_orphaned_tool_result(
     for j in range(len(sanitized_messages) - 1, -1, -1):
         prev_msg = sanitized_messages[j]
         if prev_msg.get("role") == "assistant":
+            # Check OpenAI format: tool_calls array
             tool_calls = prev_msg.get("tool_calls")
             if tool_calls:
                 for tool_call in cast(list, tool_calls):
@@ -2231,6 +2232,16 @@ def _is_orphaned_tool_result(
                         found_matching_tool_call = True
                         break
 
+            # Check Anthropic format: content blocks with type=tool_use
+            if not found_matching_tool_call:
+                content = prev_msg.get("content")
+                if isinstance(content, list):
+                    for block in content:
+                        if isinstance(block, dict) and block.get("type") == "tool_use":
+                            if block.get("id") == tool_call_id:
+                                found_matching_tool_call = True
+                                break
+
             break
 
     if not found_matching_tool_call:

litellm/types/llms/openai.py

@@ -797,7 +797,8 @@ ValidUserMessageContentTypes = [
     "guarded_text",
     "video_url",
     "file",
-]  # used for validating user messages. Prevent users from accidentally sending anthropic messages.
+    "tool_result",
+]  # used for validating user messages. Includes tool_result for Anthropic-format content blocks.
 
 ValidUserMessageContentTypesLiteral = Literal[
     "text",
@@ -808,6 +809,7 @@ ValidUserMessageContentTypesLiteral = Literal[
     "guarded_text",
     "video_url",
     "file",
+    "tool_result",
 ]
 
 ValidUserMessageContentTypes = [
@@ -819,7 +821,8 @@ ValidUserMessageContentTypes = [
     "guarded_text",
     "video_url",
     "file",
-]  # used for validating user messages. Prevent users from accidentally sending anthropic messages.
+    "tool_result",
+]  # used for validating user messages. Includes tool_result for Anthropic-format content blocks.
 
 # Assistant message content types (text, thinking, redacted_thinking, image_url)
 ValidAssistantMessageContentTypesLiteral = Literal[

tests/test_litellm/llms/anthropic/test_anthropic_tool_content.py

@@ -0,0 +1,110 @@
+"""
+Tests for Anthropic-format tool_use handling in sanitization and user-message validation.
+
+Covers:
+- _is_orphaned_tool_result matching prior assistant tool_use content blocks
+- validate_chat_completion_user_messages accepting tool_result content blocks in user messages
+"""
+
+import os
+import sys
+
+import pytest
+
+sys.path.insert(
+    0, os.path.abspath(os.path.join(os.path.dirname(__file__), "../../../.."))
+)
+
+from litellm.litellm_core_utils.prompt_templates.factory import _is_orphaned_tool_result
+from litellm.types.llms.openai import ValidUserMessageContentTypes
+from litellm.utils import validate_chat_completion_user_messages
+
+
+class TestIsOrphanedToolResultAnthropicFormat:
+    """_is_orphaned_tool_result with Anthropic-format tool_use content blocks."""
+
+    def test_not_orphaned_when_anthropic_tool_use_present(self):
+        """Tool message is not orphaned when the latest assistant has a matching tool_use block."""
+        sanitized_messages = [
+            {
+                "role": "assistant",
+                "content": [
+                    {"type": "text", "text": "Let me check that."},
+                    {
+                        "type": "tool_use",
+                        "id": "call_123",
+                        "name": "get_weather",
+                        "input": {"city": "SF"},
+                    },
+                ],
+            }
+        ]
+        current_message = {
+            "role": "tool",
+            "tool_call_id": "call_123",
+            "content": "72F sunny",
+        }
+        assert _is_orphaned_tool_result(current_message, sanitized_messages) is False
+
+    def test_orphaned_when_no_tool_use_in_assistant(self):
+        """Tool message is orphaned when the latest assistant has no tool_calls or tool_use."""
+        sanitized_messages = [
+            {
+                "role": "assistant",
+                "content": "Just a plain text response",
+            }
+        ]
+        current_message = {
+            "role": "tool",
+            "tool_call_id": "call_456",
+            "content": "result data",
+        }
+        assert _is_orphaned_tool_result(current_message, sanitized_messages) is True
+
+    def test_not_orphaned_with_openai_format_tool_calls(self):
+        """Tool message is not orphaned when the assistant uses OpenAI-format tool_calls."""
+        sanitized_messages = [
+            {
+                "role": "assistant",
+                "content": None,
+                "tool_calls": [
+                    {
+                        "id": "call_789",
+                        "type": "function",
+                        "function": {"name": "search", "arguments": "{}"},
+                    }
+                ],
+            }
+        ]
+        current_message = {
+            "role": "tool",
+            "tool_call_id": "call_789",
+            "content": "search results",
+        }
+        assert _is_orphaned_tool_result(current_message, sanitized_messages) is False
+
+
+class TestToolResultUserMessageValidation:
+    """validate_chat_completion_user_messages with Anthropic-style tool_result blocks."""
+
+    def test_tool_result_in_valid_types(self):
+        """tool_result is an allowed user content type for mixed Anthropic-style payloads."""
+        assert "tool_result" in ValidUserMessageContentTypes
+
+    def test_validate_accepts_tool_result_in_user_message(self):
+        """User messages may include type=tool_result content blocks (e.g. Cursor / Anthropic)."""
+        messages = [
+            {
+                "role": "user",
+                "content": [
+                    {"type": "text", "text": "Here is the tool output."},
+                    {
+                        "type": "tool_result",
+                        "tool_use_id": "call_abc",
+                        "content": "ok",
+                    },
+                ],
+            }
+        ]
+        out = validate_chat_completion_user_messages(messages)
+        assert out == messages