fix(anthropic): strip Gemini thought suffix from streaming tool_use id

Gemini tool call ids embed thought signatures as call_*__thought__*; the
Anthropic /v1/messages SSE adapter now exposes a clean id and moves the
signature to provider_specific_fields.signature for round-trip.

Fixes #25836.

Made-with: Cursor

litellm/llms/anthropic/experimental_pass_through/adapters/transformation.py

@@ -72,6 +72,9 @@ from openai.types.chat.chat_completion_chunk import Choice as OpenAIStreamingCho
 from litellm.litellm_core_utils.prompt_templates.common_utils import (
     parse_tool_call_arguments,
 )
+from litellm.litellm_core_utils.prompt_templates.factory import (
+    THOUGHT_SIGNATURE_SEPARATOR,
+)
 from litellm.types.llms.anthropic import (
     ANTHROPIC_HOSTED_TOOLS,
     AllAnthropicToolsValues,
@@ -1366,7 +1369,7 @@ class LiteLLMAnthropicMessagesAdapter:
         "ContentBlockContentBlockDict",
     ]:
         from litellm._uuid import uuid
-        from litellm.types.llms.anthropic import TextBlock, ToolUseBlock
+        from litellm.types.llms.anthropic import TextBlock
 
         for choice in choices:
             if (
@@ -1374,12 +1377,25 @@ class LiteLLMAnthropicMessagesAdapter:
                 and len(choice.delta.tool_calls) > 0
                 and choice.delta.tool_calls[0].function is not None
             ):
-                return "tool_use", ToolUseBlock(
-                    type="tool_use",
-                    id=choice.delta.tool_calls[0].id or str(uuid.uuid4()),
-                    name=choice.delta.tool_calls[0].function.name or "",
-                    input={},  # type: ignore[typeddict-item]
-                )
+                raw_id = choice.delta.tool_calls[0].id or str(uuid.uuid4())
+                tool_name = choice.delta.tool_calls[0].function.name or ""
+                base_id = raw_id
+                thought_sig: Optional[str] = None
+                if THOUGHT_SIGNATURE_SEPARATOR in raw_id:
+                    parts = raw_id.split(THOUGHT_SIGNATURE_SEPARATOR, 1)
+                    base_id = parts[0]
+                    thought_sig = parts[1] if len(parts) > 1 else None
+                tool_block: Dict[str, Any] = {
+                    "type": "tool_use",
+                    "id": base_id,
+                    "name": tool_name,
+                    "input": {},
+                }
+                if thought_sig:
+                    tool_block["provider_specific_fields"] = {
+                        "signature": thought_sig,
+                    }
+                return "tool_use", cast("ContentBlockContentBlockDict", tool_block)
             elif choice.delta.content is not None and len(choice.delta.content) > 0:
                 return "text", TextBlock(type="text", text="")
             elif isinstance(choice, StreamingChoices) and hasattr(

tests/test_litellm/llms/anthropic/experimental_pass_through/adapters/test_anthropic_experimental_pass_through_adapters_transformation.py

@@ -7,6 +7,9 @@ import pytest
 sys.path.insert(0, os.path.abspath("../../../../.."))
 
 
+from litellm.litellm_core_utils.prompt_templates.factory import (
+    THOUGHT_SIGNATURE_SEPARATOR,
+)
 from litellm.llms.anthropic.experimental_pass_through.adapters.transformation import (
     OPENAI_MAX_TOOL_NAME_LENGTH,
     LiteLLMAnthropicMessagesAdapter,
@@ -74,6 +77,50 @@ def test_translate_streaming_openai_chunk_to_anthropic_content_block():
     }
 
 
+def test_translate_streaming_openai_chunk_strips_gemini_thought_from_tool_call_id():
+    """Gemini embeds thought signatures in OpenAI tool ids; Anthropic SSE should expose a clean id."""
+    base = "call_3e9417b7925e49aca9a71dc1885e"
+    sig = "CiIBDDnWx"
+    combined = f"{base}{THOUGHT_SIGNATURE_SEPARATOR}{sig}"
+    choices = [
+        StreamingChoices(
+            finish_reason=None,
+            index=0,
+            delta=Delta(
+                provider_specific_fields=None,
+                content=None,
+                role="assistant",
+                function_call=None,
+                tool_calls=[
+                    ChatCompletionDeltaToolCall(
+                        id=combined,
+                        function=Function(
+                            arguments='{"a": 17, "b": 25}', name="add_numbers"
+                        ),
+                        type="function",
+                        index=0,
+                    )
+                ],
+                audio=None,
+            ),
+            logprobs=None,
+        )
+    ]
+
+    (
+        block_type,
+        content_block_start,
+    ) = LiteLLMAnthropicMessagesAdapter()._translate_streaming_openai_chunk_to_anthropic_content_block(
+        choices=choices
+    )
+
+    assert block_type == "tool_use"
+    assert content_block_start["id"] == base
+    assert content_block_start["name"] == "add_numbers"
+    assert content_block_start["input"] == {}
+    assert content_block_start["provider_specific_fields"]["signature"] == sig
+
+
 def test_translate_streaming_openai_chunk_to_anthropic_thinking_content_block():
     choices = [
         StreamingChoices(