diff --git a/tests/test_litellm/llms/anthropic/experimental_pass_through/adapters/test_handler_thinking_disabled.py b/tests/test_litellm/llms/anthropic/experimental_pass_through/adapters/test_handler_thinking_disabled.py
new file mode 100644
index 00000000000..43233b4e880
--- /dev/null
+++ b/tests/test_litellm/llms/anthropic/experimental_pass_through/adapters/test_handler_thinking_disabled.py
@@ -0,0 +1,205 @@
+"""Handler-level tests for ``thinking_disabled`` computation and threading.
+
+Covers the boolean logic that decides whether thinking is disabled
+(``thinking is None or thinking.type == "disabled"``) and verifies it is
+threaded correctly to ``ANTHROPIC_ADAPTER`` output-translation calls for
+both the async and sync handler entry points, in streaming and non-streaming
+modes.
+
+Mocks ``litellm.acompletion`` / ``litellm.completion`` and
+``ANTHROPIC_ADAPTER`` directly, alongside the preparation helpers that run
+before the ``thinking_disabled`` computation, so the tests are focused on
+the computation and threading rather than the full request pipeline.
+"""
+
+import pytest
+from unittest.mock import MagicMock, patch
+
+from litellm.llms.anthropic.experimental_pass_through.adapters.handler import (
+    LiteLLMMessagesToCompletionTransformationHandler,
+)
+
+THINKING_PARAMS = [
+    (None, True),
+    ({"type": "disabled"}, True),
+    ({"type": "enabled", "budget_tokens": 1024}, False),
+    ({"type": "adaptive"}, False),
+]
+
+MESSAGES = [{"role": "user", "content": "hello"}]
+
+
+# ---------------------------------------------------------------------------
+# Async handler — streaming
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.parametrize(
+    "thinking_param,expected_thinking_disabled",
+    THINKING_PARAMS,
+)
+async def test_async_handler_streaming_threads_thinking_disabled(
+    thinking_param, expected_thinking_disabled
+):
+    """Async handler, stream=True: ``thinking_disabled`` reaches the streaming
+    adapter call."""
+    with (
+        patch(
+            "litellm.llms.anthropic.experimental_pass_through.adapters.handler._prepare_context_managed_request",
+            return_value=None,
+        ),
+        patch.object(
+            LiteLLMMessagesToCompletionTransformationHandler,
+            "_prepare_completion_kwargs",
+            return_value=({}, {}),
+        ),
+        patch("litellm.acompletion", return_value=MagicMock()),
+        patch(
+            "litellm.llms.anthropic.experimental_pass_through.adapters.handler.ANTHROPIC_ADAPTER"
+        ) as mock_adapter,
+    ):
+        mock_adapter.translate_completion_output_params_streaming.return_value = iter([])
+        await LiteLLMMessagesToCompletionTransformationHandler.async_anthropic_messages_handler(
+            max_tokens=100,
+            messages=MESSAGES,
+            model="gpt-4o",
+            stream=True,
+            thinking=thinking_param,
+        )
+        call_kwargs = (
+            mock_adapter.translate_completion_output_params_streaming.call_args.kwargs
+        )
+        assert (
+            call_kwargs.get("thinking_disabled") is expected_thinking_disabled
+        ), f"thinking={thinking_param!r}: expected thinking_disabled={expected_thinking_disabled}"
+
+
+# ---------------------------------------------------------------------------
+# Async handler — non-streaming
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.parametrize(
+    "thinking_param,expected_thinking_disabled",
+    THINKING_PARAMS,
+)
+async def test_async_handler_non_streaming_threads_thinking_disabled(
+    thinking_param, expected_thinking_disabled
+):
+    """Async handler, stream=False: ``thinking_disabled`` reaches the
+    non-streaming adapter call."""
+    with (
+        patch(
+            "litellm.llms.anthropic.experimental_pass_through.adapters.handler._prepare_context_managed_request",
+            return_value=None,
+        ),
+        patch.object(
+            LiteLLMMessagesToCompletionTransformationHandler,
+            "_prepare_completion_kwargs",
+            return_value=({}, {}),
+        ),
+        patch("litellm.acompletion", return_value=MagicMock()),
+        patch(
+            "litellm.llms.anthropic.experimental_pass_through.adapters.handler.ANTHROPIC_ADAPTER"
+        ) as mock_adapter,
+    ):
+        mock_adapter.translate_completion_output_params.return_value = MagicMock()
+        await LiteLLMMessagesToCompletionTransformationHandler.async_anthropic_messages_handler(
+            max_tokens=100,
+            messages=MESSAGES,
+            model="gpt-4o",
+            stream=False,
+            thinking=thinking_param,
+        )
+        call_kwargs = mock_adapter.translate_completion_output_params.call_args.kwargs
+        assert (
+            call_kwargs.get("thinking_disabled") is expected_thinking_disabled
+        ), f"thinking={thinking_param!r}: expected thinking_disabled={expected_thinking_disabled}"
+
+
+# ---------------------------------------------------------------------------
+# Sync handler — streaming
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.parametrize(
+    "thinking_param,expected_thinking_disabled",
+    THINKING_PARAMS,
+)
+def test_sync_handler_streaming_threads_thinking_disabled(
+    thinking_param, expected_thinking_disabled
+):
+    """Sync handler, stream=True: ``thinking_disabled`` reaches the streaming
+    adapter call.
+
+    Uses the direct synchronous path (no ``context_management``, no compaction
+    blocks) so ``run_async_function`` is never invoked.
+    """
+    with (
+        patch.object(
+            LiteLLMMessagesToCompletionTransformationHandler,
+            "_prepare_completion_kwargs",
+            return_value=({}, {}),
+        ),
+        patch("litellm.completion", return_value=MagicMock()),
+        patch(
+            "litellm.llms.anthropic.experimental_pass_through.adapters.handler.ANTHROPIC_ADAPTER"
+        ) as mock_adapter,
+    ):
+        mock_adapter.translate_completion_output_params_streaming.return_value = iter([])
+        LiteLLMMessagesToCompletionTransformationHandler.anthropic_messages_handler(
+            max_tokens=100,
+            messages=MESSAGES,
+            model="gpt-4o",
+            stream=True,
+            thinking=thinking_param,
+        )
+        call_kwargs = (
+            mock_adapter.translate_completion_output_params_streaming.call_args.kwargs
+        )
+        assert (
+            call_kwargs.get("thinking_disabled") is expected_thinking_disabled
+        ), f"thinking={thinking_param!r}: expected thinking_disabled={expected_thinking_disabled}"
+
+
+# ---------------------------------------------------------------------------
+# Sync handler — non-streaming
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.parametrize(
+    "thinking_param,expected_thinking_disabled",
+    THINKING_PARAMS,
+)
+def test_sync_handler_non_streaming_threads_thinking_disabled(
+    thinking_param, expected_thinking_disabled
+):
+    """Sync handler, stream=False: ``thinking_disabled`` reaches the
+    non-streaming adapter call.
+
+    Uses the direct synchronous path (no ``context_management``, no compaction
+    blocks) so ``run_async_function`` is never invoked.
+    """
+    with (
+        patch.object(
+            LiteLLMMessagesToCompletionTransformationHandler,
+            "_prepare_completion_kwargs",
+            return_value=({}, {}),
+        ),
+        patch("litellm.completion", return_value=MagicMock()),
+        patch(
+            "litellm.llms.anthropic.experimental_pass_through.adapters.handler.ANTHROPIC_ADAPTER"
+        ) as mock_adapter,
+    ):
+        mock_adapter.translate_completion_output_params.return_value = MagicMock()
+        LiteLLMMessagesToCompletionTransformationHandler.anthropic_messages_handler(
+            max_tokens=100,
+            messages=MESSAGES,
+            model="gpt-4o",
+            stream=False,
+            thinking=thinking_param,
+        )
+        call_kwargs = mock_adapter.translate_completion_output_params.call_args.kwargs
+        assert (
+            call_kwargs.get("thinking_disabled") is expected_thinking_disabled
+        ), f"thinking={thinking_param!r}: expected thinking_disabled={expected_thinking_disabled}"