From e3fb8b1f1f5189cd08819d6edcf2aba8818b8b3a Mon Sep 17 00:00:00 2001
From: jesco-absolut <team@srswti.com>
Date: Sat, 1 Aug 2026 16:54:28 -0400
Subject: [PATCH] fix(anthropic): reduce reasoning fallback complexity

---
 .../adapters/transformation.py                | 45 ++++++++++---------
 1 file changed, 25 insertions(+), 20 deletions(-)

diff --git a/litellm/llms/anthropic/experimental_pass_through/adapters/transformation.py b/litellm/llms/anthropic/experimental_pass_through/adapters/transformation.py
index 4c6df5002dc..4c78a6c3876 100644
--- a/litellm/llms/anthropic/experimental_pass_through/adapters/transformation.py
+++ b/litellm/llms/anthropic/experimental_pass_through/adapters/transformation.py
@@ -1426,6 +1426,28 @@ class LiteLLMAnthropicMessagesAdapter:
 
         return "text", TextBlock(type="text", text="")
 
+    @staticmethod
+    def _streaming_reasoning_fields(choice: StreamingChoices) -> tuple[str, str]:
+        reasoning_content = ""
+        reasoning_signature = ""
+        thinking_blocks = getattr(choice.delta, "thinking_blocks", None) or []
+        for thinking_block in thinking_blocks:
+            if thinking_block["type"] == "thinking":
+                thinking = thinking_block.get("thinking") or ""
+                signature = thinking_block.get("signature") or ""
+
+                assert isinstance(thinking, str)
+                assert isinstance(signature, str)
+
+                reasoning_content += thinking
+                reasoning_signature += signature
+
+        if reasoning_content or reasoning_signature:
+            return reasoning_content, reasoning_signature
+
+        fallback = getattr(choice.delta, "reasoning_content", None)
+        return fallback or "", ""
+
     def _translate_streaming_openai_chunk_to_anthropic(
         self, choices: List[Union[OpenAIStreamingChoice, StreamingChoices]]
     ) -> Tuple[
@@ -1450,26 +1472,9 @@ class LiteLLMAnthropicMessagesAdapter:
                     if tool.function is not None and tool.function.arguments is not None:
                         partial_json = (partial_json or "") + tool.function.arguments
             elif isinstance(choice, StreamingChoices):
-                thinking_blocks = getattr(choice.delta, "thinking_blocks", None) or []
-                choice_reasoning_content = ""
-                choice_reasoning_signature = ""
-                if len(thinking_blocks) > 0:
-                    for thinking_block in thinking_blocks:
-                        if thinking_block["type"] == "thinking":
-                            thinking = thinking_block.get("thinking") or ""
-                            signature = thinking_block.get("signature") or ""
-
-                            assert isinstance(thinking, str)
-                            assert isinstance(signature, str)
-
-                            choice_reasoning_content += thinking
-                            choice_reasoning_signature += signature
-                if choice_reasoning_content or choice_reasoning_signature:
-                    reasoning_content += choice_reasoning_content
-                    reasoning_signature += choice_reasoning_signature
-                elif hasattr(choice.delta, "reasoning_content"):
-                    if choice.delta.reasoning_content is not None:
-                        reasoning_content += choice.delta.reasoning_content
+                choice_reasoning_content, choice_reasoning_signature = self._streaming_reasoning_fields(choice)
+                reasoning_content += choice_reasoning_content
+                reasoning_signature += choice_reasoning_signature
 
         if partial_json is not None:
             return "input_json_delta", ContentJsonBlockDelta(type="input_json_delta", partial_json=partial_json)