diff --git a/litellm/llms/bedrock/chat/invoke_transformations/anthropic_claude3_transformation.py b/litellm/llms/bedrock/chat/invoke_transformations/anthropic_claude3_transformation.py
index 2a4c38e71ea..07ddf6570f2 100644
--- a/litellm/llms/bedrock/chat/invoke_transformations/anthropic_claude3_transformation.py
+++ b/litellm/llms/bedrock/chat/invoke_transformations/anthropic_claude3_transformation.py
@@ -107,6 +107,11 @@ class AmazonAnthropicClaudeConfig(AmazonInvokeConfig, AnthropicConfig):
         # Restore original model name
         model = original_model
 
+        # The stub model hides the original model from the parent's legacy thinking upgrade
+        AnthropicModelInfo.translate_legacy_thinking_for_adaptive_model(
+            model=original_model, optional_params=optional_params, custom_llm_provider="bedrock"
+        )
+
         # The stub model hides the original model from the parent's forced-tool-use backstop
         response_format_tool_choice: Final = optional_params.get("tool_choice")
         if (
diff --git a/tests/test_litellm/llms/bedrock/chat/invoke_transformations/test_bedrock_chat_invoke_transformations_anthropic_claude3_transformation.py b/tests/test_litellm/llms/bedrock/chat/invoke_transformations/test_bedrock_chat_invoke_transformations_anthropic_claude3_transformation.py
index 41d82e4f960..d136cb6450b 100644
--- a/tests/test_litellm/llms/bedrock/chat/invoke_transformations/test_bedrock_chat_invoke_transformations_anthropic_claude3_transformation.py
+++ b/tests/test_litellm/llms/bedrock/chat/invoke_transformations/test_bedrock_chat_invoke_transformations_anthropic_claude3_transformation.py
@@ -671,3 +671,22 @@ def test_bedrock_chat_invoke_fable_5_1_response_format_avoids_forced_tool_choice
     assert "output_format" not in result
     assert "tools" in result
     assert "tool_choice" not in result
+
+
+def test_bedrock_chat_invoke_response_format_stub_still_upgrades_legacy_thinking(local_model_cost_map):
+    """Regression: the tool-based ``response_format`` path swaps in a Claude 3 stub
+    model before the shared Anthropic mapping, which hid the adaptive-only model
+    from the legacy ``thinking`` upgrade and left ``type=enabled`` on the wire."""
+    result = AmazonAnthropicClaudeConfig().map_openai_params(
+        non_default_params={
+            "response_format": {"type": "json_object"},
+            "thinking": {"type": "enabled", "budget_tokens": 4096},
+            "max_tokens": 8192,
+        },
+        optional_params={},
+        model="us.anthropic.claude-fable-5-1",
+        drop_params=False,
+    )
+
+    assert result["thinking"] == {"type": "adaptive"}
+    assert result["output_config"] == {"effort": "high"}