From 29126ea4dea5d630ca3fb9d6e8d2a8462bf9784c Mon Sep 17 00:00:00 2001
From: adhavan18 <sk.tamiladhavan@gmail.com>
Date: Thu, 24 Sep 2026 09:16:26 +0530
Subject: [PATCH] fix(adapter): gate thinking blocks by target

---
 .../adapters/transformation.py                |  8 +++-
 ...al_pass_through_adapters_transformation.py | 48 +++++++++++++++++++
 2 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/litellm/llms/anthropic/experimental_pass_through/adapters/transformation.py b/litellm/llms/anthropic/experimental_pass_through/adapters/transformation.py
index 85431a5a637..d3e24cdd11d 100644
--- a/litellm/llms/anthropic/experimental_pass_through/adapters/transformation.py
+++ b/litellm/llms/anthropic/experimental_pass_through/adapters/transformation.py
@@ -625,11 +625,15 @@ class LiteLLMAnthropicMessagesAdapter:
                 assistant_message = ChatCompletionAssistantMessage(
                     role="assistant",
                     content=assistant_content,
-                    thinking_blocks=(thinking_blocks if len(thinking_blocks) > 0 else None),
                 )
                 if len(tool_calls) > 0:
                     assistant_message["tool_calls"] = tool_calls
-                if len(thinking_blocks) > 0:
+                if len(thinking_blocks) > 0 and (
+                    model is None
+                    or LiteLLMAnthropicMessagesAdapter.is_anthropic_claude_model(
+                        model
+                    )
+                ):
                     assistant_message["thinking_blocks"] = thinking_blocks
                 reasoning_content = reasoning_content_from_thinking_blocks(thinking_blocks)
                 if reasoning_content:
diff --git a/tests/test_litellm/llms/anthropic/experimental_pass_through/adapters/test_anthropic_experimental_pass_through_adapters_transformation.py b/tests/test_litellm/llms/anthropic/experimental_pass_through/adapters/test_anthropic_experimental_pass_through_adapters_transformation.py
index d03174bc2c6..92383e3d621 100644
--- a/tests/test_litellm/llms/anthropic/experimental_pass_through/adapters/test_anthropic_experimental_pass_through_adapters_transformation.py
+++ b/tests/test_litellm/llms/anthropic/experimental_pass_through/adapters/test_anthropic_experimental_pass_through_adapters_transformation.py
@@ -481,6 +481,54 @@ def test_translate_anthropic_messages_to_openai_thinking_blocks():
     assert result[1]["tool_calls"][0]["id"] == "toolu_01234"
 
 
+def test_translate_anthropic_messages_to_openai_keeps_thinking_blocks_for_claude():
+    anthropic_messages = [
+        AnthopicMessagesAssistantMessageParam(
+            role="assistant",
+            content=[
+                {
+                    "type": "thinking",
+                    "thinking": "My reasoning here.",
+                    "signature": "sig123",
+                },
+                {"type": "text", "text": "Answer text."},
+            ],
+        )
+    ]
+
+    result = LiteLLMAnthropicMessagesAdapter().translate_anthropic_messages_to_openai(
+        messages=anthropic_messages,
+        model="anthropic/claude-sonnet-4-5",
+    )
+
+    assert result[0]["thinking_blocks"][0]["thinking"] == "My reasoning here."
+    assert result[0]["reasoning_content"] == "My reasoning here."
+
+
+def test_translate_anthropic_messages_to_openai_omits_thinking_blocks_for_non_claude():
+    anthropic_messages = [
+        AnthopicMessagesAssistantMessageParam(
+            role="assistant",
+            content=[
+                {
+                    "type": "thinking",
+                    "thinking": "My reasoning here.",
+                    "signature": "sig123",
+                },
+                {"type": "text", "text": "Answer text."},
+            ],
+        )
+    ]
+
+    result = LiteLLMAnthropicMessagesAdapter().translate_anthropic_messages_to_openai(
+        messages=anthropic_messages,
+        model="openai/my-vllm-model",
+    )
+
+    assert "thinking_blocks" not in result[0]
+    assert result[0]["reasoning_content"] == "My reasoning here."
+
+
 def test_translate_anthropic_messages_to_openai_drops_bridge_encrypted_reasoning_blocks():
     """A session that moves from an OpenAI reasoning model to a chat provider replays reasoning only OpenAI can read.