diff --git a/libs/partners/anthropic/langchain_anthropic/chat_models.py b/libs/partners/anthropic/langchain_anthropic/chat_models.py
index d7e63c8c04..ce0f3bb98a 100644
--- a/libs/partners/anthropic/langchain_anthropic/chat_models.py
+++ b/libs/partners/anthropic/langchain_anthropic/chat_models.py
@@ -104,7 +104,12 @@ def _merge_messages(
     for curr in messages:
         curr = curr.copy(deep=True)
         if isinstance(curr, ToolMessage):
-            if isinstance(curr.content, str):
+            if isinstance(curr.content, list) and all(
+                isinstance(block, dict) and block.get("type") == "tool_result"
+                for block in curr.content
+            ):
+                curr = HumanMessage(curr.content)  # type: ignore[misc]
+            else:
                 curr = HumanMessage(  # type: ignore[misc]
                     [
                         {
@@ -114,8 +119,6 @@ def _merge_messages(
                         }
                     ]
                 )
-            else:
-                curr = HumanMessage(curr.content)  # type: ignore[misc]
         last = merged[-1] if merged else None
         if isinstance(last, HumanMessage) and isinstance(curr, HumanMessage):
             if isinstance(last.content, str):
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 31d12db98c..d7e21edb9a 100644
--- a/libs/partners/anthropic/tests/unit_tests/test_chat_models.py
+++ b/libs/partners/anthropic/tests/unit_tests/test_chat_models.py
@@ -140,7 +140,19 @@ def test__merge_messages() -> None:
             ]
         ),
         ToolMessage("buz output", tool_call_id="1"),  # type: ignore[misc]
-        ToolMessage("blah output", tool_call_id="2"),  # type: ignore[misc]
+        ToolMessage(
+            content=[
+                {
+                    "type": "image",
+                    "source": {
+                        "type": "base64",
+                        "media_type": "image/jpeg",
+                        "data": "fake_image_data",
+                    },
+                },
+            ],
+            tool_call_id="2",
+        ),  # type: ignore[misc]
         HumanMessage("next thing"),  # type: ignore[misc]
     ]
     expected = [
@@ -169,7 +181,20 @@ def test__merge_messages() -> None:
         HumanMessage(  # type: ignore[misc]
             [
                 {"type": "tool_result", "content": "buz output", "tool_use_id": "1"},
-                {"type": "tool_result", "content": "blah output", "tool_use_id": "2"},
+                {
+                    "type": "tool_result",
+                    "content": [
+                        {
+                            "type": "image",
+                            "source": {
+                                "type": "base64",
+                                "media_type": "image/jpeg",
+                                "data": "fake_image_data",
+                            },
+                        },
+                    ],
+                    "tool_use_id": "2",
+                },
                 {"type": "text", "text": "next thing"},
             ]
         ),
@@ -177,6 +202,27 @@ def test__merge_messages() -> None:
     actual = _merge_messages(messages)
     assert expected == actual
 
+    # Test tool message case
+    messages = [
+        ToolMessage("buz output", tool_call_id="1"),  # type: ignore[misc]
+        ToolMessage(  # type: ignore[misc]
+            content=[
+                {"type": "tool_result", "content": "blah output", "tool_use_id": "2"}
+            ],
+            tool_call_id="2",
+        ),
+    ]
+    expected = [
+        HumanMessage(  # type: ignore[misc]
+            [
+                {"type": "tool_result", "content": "buz output", "tool_use_id": "1"},
+                {"type": "tool_result", "content": "blah output", "tool_use_id": "2"},
+            ]
+        )
+    ]
+    actual = _merge_messages(messages)
+    assert expected == actual
+
 
 def test__merge_messages_mutation() -> None:
     original_messages = [