From f2d1c0eb22ed8f7e0f4ddf40bdb878ef192bad98 Mon Sep 17 00:00:00 2001
From: Sameer Kankute <sameer@berri.ai>
Date: Fri, 6 Feb 2026 09:24:43 +0530
Subject: [PATCH] Add adaptive thinking support for anthropic opus 4.6

---
 litellm/llms/anthropic/chat/transformation.py | 19 +++--
 .../test_anthropic_chat_transformation.py     | 69 +++++++++++++++++++
 2 files changed, 78 insertions(+), 10 deletions(-)

diff --git a/litellm/llms/anthropic/chat/transformation.py b/litellm/llms/anthropic/chat/transformation.py
index 82eccee596d..a8254833d36 100644
--- a/litellm/llms/anthropic/chat/transformation.py
+++ b/litellm/llms/anthropic/chat/transformation.py
@@ -170,9 +170,9 @@ class AnthropicConfig(AnthropicModelInfo, BaseConfig):
             tool_call["caller"] = cast(Dict[str, Any], anthropic_tool_content["caller"])  # type: ignore[typeddict-item]
         return tool_call
 
-    def _is_claude_opus_4_5(self, model: str) -> bool:
+    def _is_claude_opus_4_6(self, model: str) -> bool:
         """Check if the model is Claude Opus 4.5."""
-        return "opus-4-5" in model.lower() or "opus_4_5" in model.lower()
+        return "opus-4-6" in model.lower() or "opus_4_6" in model.lower()
 
     def get_supported_openai_params(self, model: str):
         params = [
@@ -851,14 +851,13 @@ class AnthropicConfig(AnthropicModelInfo, BaseConfig):
             if param == "thinking":
                 optional_params["thinking"] = value
             elif param == "reasoning_effort" and isinstance(value, str):
-                # For Claude Opus 4.5, map reasoning_effort to output_config
-                if self._is_claude_opus_4_5(model):
-                    optional_params["output_config"] = {"effort": value}
-
-                # For other models, map to thinking parameter
-                optional_params["thinking"] = AnthropicConfig._map_reasoning_effort(
-                    value
-                )
+                # For Claude Opus 4.6, map reasoning_effort to new adaptive thinking type
+                if self._is_claude_opus_4_6(model):
+                    optional_params["thinking"] = {"type": "adaptive"}
+                else:
+                    optional_params["thinking"] = AnthropicConfig._map_reasoning_effort(
+                        value
+                    )
             elif param == "web_search_options" and isinstance(value, dict):
                 hosted_web_search_tool = self.map_web_search_tool(
                     cast(OpenAIWebSearchOptions, value)
diff --git a/tests/test_litellm/llms/anthropic/chat/test_anthropic_chat_transformation.py b/tests/test_litellm/llms/anthropic/chat/test_anthropic_chat_transformation.py
index 7e96c4634fd..afe4fb6273b 100644
--- a/tests/test_litellm/llms/anthropic/chat/test_anthropic_chat_transformation.py
+++ b/tests/test_litellm/llms/anthropic/chat/test_anthropic_chat_transformation.py
@@ -1881,6 +1881,75 @@ def test_calculate_usage_completion_tokens_details_with_reasoning():
     assert usage.completion_tokens == 500
 
 
+# ============ Reasoning Effort Tests ============
+
+
+def test_reasoning_effort_maps_to_adaptive_thinking_for_opus_4_6():
+    """
+    Test that reasoning_effort maps to adaptive thinking type for Claude Opus 4.6.
+    
+    For Claude Opus 4.6, reasoning_effort should map to {"type": "adaptive"} 
+    regardless of the effort level specified.
+    """
+    config = AnthropicConfig()
+    
+    # Test with different reasoning_effort values - all should map to adaptive
+    for effort in ["low", "medium", "high", "minimal"]:
+        non_default_params = {"reasoning_effort": effort}
+        optional_params = {}
+        
+        result = config.map_openai_params(
+            non_default_params=non_default_params,
+            optional_params=optional_params,
+            model="claude-opus-4-6-20250514",
+            drop_params=False
+        )
+        
+        # Should map to adaptive thinking type
+        assert "thinking" in result
+        assert result["thinking"]["type"] == "adaptive"
+        # Should not have budget_tokens for adaptive type
+        assert "budget_tokens" not in result["thinking"]
+        # reasoning_effort should not be in the result (it's transformed to thinking)
+        assert "reasoning_effort" not in result
+
+
+def test_reasoning_effort_maps_to_budget_thinking_for_non_opus_4_6():
+    """
+    Test that reasoning_effort maps to budget-based thinking config for non-Opus 4.6 models.
+    
+    For models other than Claude Opus 4.6, reasoning_effort should map to 
+    thinking config with budget_tokens based on the effort level.
+    """
+    config = AnthropicConfig()
+    
+    # Test with Claude Sonnet 4.5 (non-Opus 4.6 model)
+    test_cases = [
+        ("low", 1024),      # DEFAULT_REASONING_EFFORT_LOW_THINKING_BUDGET
+        ("medium", 2048),   # DEFAULT_REASONING_EFFORT_MEDIUM_THINKING_BUDGET
+        ("high", 4096),     # DEFAULT_REASONING_EFFORT_HIGH_THINKING_BUDGET
+        ("minimal", 128),   # DEFAULT_REASONING_EFFORT_MINIMAL_THINKING_BUDGET
+    ]
+    
+    for effort, expected_budget in test_cases:
+        non_default_params = {"reasoning_effort": effort}
+        optional_params = {}
+        
+        result = config.map_openai_params(
+            non_default_params=non_default_params,
+            optional_params=optional_params,
+            model="claude-sonnet-4-5-20250929",
+            drop_params=False
+        )
+        
+        # Should map to enabled thinking type with budget_tokens
+        assert "thinking" in result
+        assert result["thinking"]["type"] == "enabled"
+        assert result["thinking"]["budget_tokens"] == expected_budget
+        # reasoning_effort should not be in the result (it's transformed to thinking)
+        assert "reasoning_effort" not in result
+
+
 def test_code_execution_tool_results_extraction():
     """
     Test that code execution tool results (bash_code_execution_tool_result,