diff --git a/libs/partners/anthropic/langchain_anthropic/chat_models.py b/libs/partners/anthropic/langchain_anthropic/chat_models.py
index 28f57e1ccea..35463c88a74 100644
--- a/libs/partners/anthropic/langchain_anthropic/chat_models.py
+++ b/libs/partners/anthropic/langchain_anthropic/chat_models.py
@@ -250,15 +250,31 @@ def _merge_messages(
             ):
                 curr = HumanMessage(curr.content)  # type: ignore[misc]
             else:
+                tool_content = curr.content
+                cache_ctrl = None
+                # Extract cache_control from content blocks and hoist it
+                # to the tool_result level.  Anthropic's API does not
+                # support cache_control on tool_result content sub-blocks.
+                if isinstance(tool_content, list):
+                    cleaned = []
+                    for block in tool_content:
+                        if isinstance(block, dict) and "cache_control" in block:
+                            cache_ctrl = block["cache_control"]
+                            block = {
+                                k: v for k, v in block.items() if k != "cache_control"
+                            }
+                        cleaned.append(block)
+                    tool_content = cleaned
+                tool_result: dict = {
+                    "type": "tool_result",
+                    "content": tool_content,
+                    "tool_use_id": curr.tool_call_id,
+                    "is_error": curr.status == "error",
+                }
+                if cache_ctrl:
+                    tool_result["cache_control"] = cache_ctrl
                 curr = HumanMessage(  # type: ignore[misc]
-                    [
-                        {
-                            "type": "tool_result",
-                            "content": curr.content,
-                            "tool_use_id": curr.tool_call_id,
-                            "is_error": curr.status == "error",
-                        },
-                    ],
+                    [tool_result],
                 )
         last = merged[-1] if merged else None
         if any(
diff --git a/libs/partners/anthropic/tests/unit_tests/test_chat_models.py b/libs/partners/anthropic/tests/unit_tests/test_chat_models.py
index 7ac7b9ff9fb..eab0f4aed21 100644
--- a/libs/partners/anthropic/tests/unit_tests/test_chat_models.py
+++ b/libs/partners/anthropic/tests/unit_tests/test_chat_models.py
@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import copy
 import os
 from collections.abc import Callable
 from typing import Any, Literal, cast
@@ -412,6 +413,91 @@ def test__merge_messages_mutation() -> None:
     assert messages == original_messages
 
 
+def test__merge_messages_tool_message_cache_control() -> None:
+    """Test that cache_control is hoisted from content blocks to tool_result level."""
+    # Test with cache_control in content block
+    messages = [
+        ToolMessage(
+            content=[
+                {
+                    "type": "text",
+                    "text": "tool output",
+                    "cache_control": {"type": "ephemeral"},
+                }
+            ],
+            tool_call_id="1",
+        )
+    ]
+    original_messages = [copy.deepcopy(m) for m in messages]
+    expected = [
+        HumanMessage(
+            [
+                {
+                    "type": "tool_result",
+                    "content": [{"type": "text", "text": "tool output"}],
+                    "tool_use_id": "1",
+                    "is_error": False,
+                    "cache_control": {"type": "ephemeral"},
+                }
+            ]
+        )
+    ]
+    actual = _merge_messages(messages)
+    assert expected == actual
+    # Verify no mutation
+    assert messages == original_messages
+
+    # Test with multiple content blocks, cache_control on last one
+    messages = [
+        ToolMessage(
+            content=[
+                {"type": "text", "text": "first output"},
+                {
+                    "type": "text",
+                    "text": "second output",
+                    "cache_control": {"type": "ephemeral"},
+                },
+            ],
+            tool_call_id="2",
+        )
+    ]
+    expected = [
+        HumanMessage(
+            [
+                {
+                    "type": "tool_result",
+                    "content": [
+                        {"type": "text", "text": "first output"},
+                        {"type": "text", "text": "second output"},
+                    ],
+                    "tool_use_id": "2",
+                    "is_error": False,
+                    "cache_control": {"type": "ephemeral"},
+                }
+            ]
+        )
+    ]
+    actual = _merge_messages(messages)
+    assert expected == actual
+
+    # Test without cache_control
+    messages = [ToolMessage(content="simple output", tool_call_id="3")]
+    expected = [
+        HumanMessage(
+            [
+                {
+                    "type": "tool_result",
+                    "content": "simple output",
+                    "tool_use_id": "3",
+                    "is_error": False,
+                }
+            ]
+        )
+    ]
+    actual = _merge_messages(messages)
+    assert expected == actual
+
+
 def test__format_image() -> None:
     url = "dummyimage.com/600x400/000/fff"
     with pytest.raises(ValueError):