diff --git a/homeassistant/components/anthropic/entity.py b/homeassistant/components/anthropic/entity.py
index 0d07ae71432..58ca22b2ec9 100644
--- a/homeassistant/components/anthropic/entity.py
+++ b/homeassistant/components/anthropic/entity.py
@@ -600,6 +600,16 @@ class AnthropicBaseLLMEntity(Entity):
         system = chat_log.content[0]
         if not isinstance(system, conversation.SystemContent):
             raise TypeError("First message must be a system message")
+
+        # System prompt with caching enabled
+        system_prompt: list[TextBlockParam] = [
+            TextBlockParam(
+                type="text",
+                text=system.content,
+                cache_control={"type": "ephemeral"},
+            )
+        ]
+
         messages = _convert_content(chat_log.content[1:])
 
         model = options.get(CONF_CHAT_MODEL, DEFAULT[CONF_CHAT_MODEL])
@@ -608,7 +618,7 @@ class AnthropicBaseLLMEntity(Entity):
             model=model,
             messages=messages,
             max_tokens=options.get(CONF_MAX_TOKENS, DEFAULT[CONF_MAX_TOKENS]),
-            system=system.content,
+            system=system_prompt,
             stream=True,
         )
 
@@ -695,10 +705,6 @@ class AnthropicBaseLLMEntity(Entity):
                     type="auto",
                 )
 
-                if isinstance(model_args["system"], str):
-                    model_args["system"] = [
-                        TextBlockParam(type="text", text=model_args["system"])
-                    ]
                 model_args["system"].append(  # type: ignore[union-attr]
                     TextBlockParam(
                         type="text",
diff --git a/tests/components/anthropic/test_ai_task.py b/tests/components/anthropic/test_ai_task.py
index f61c9e71065..b820d199476 100644
--- a/tests/components/anthropic/test_ai_task.py
+++ b/tests/components/anthropic/test_ai_task.py
@@ -190,22 +190,23 @@ async def test_generate_data_with_attachments(
     assert user_message_with_attachments is not None
     assert isinstance(user_message_with_attachments["content"], list)
     assert len(user_message_with_attachments["content"]) == 3  # Text + attachments
-    assert user_message_with_attachments["content"] == [
-        {"type": "text", "text": "Test prompt"},
-        {
-            "type": "image",
-            "source": {
-                "data": "ZmFrZV9pbWFnZV9kYXRh",
-                "media_type": "image/jpeg",
-                "type": "base64",
-            },
-        },
-        {
-            "type": "document",
-            "source": {
-                "data": "ZmFrZV9pbWFnZV9kYXRh",
-                "media_type": "application/pdf",
-                "type": "base64",
-            },
-        },
-    ]
+
+    text_block, image_block, document_block = user_message_with_attachments["content"]
+
+    # Text block
+    assert text_block["type"] == "text"
+    assert text_block["text"] == "Test prompt"
+
+    # Image attachment
+    assert image_block["type"] == "image"
+    assert image_block["source"] == {
+        "data": "ZmFrZV9pbWFnZV9kYXRh",
+        "media_type": "image/jpeg",
+        "type": "base64",
+    }
+
+    # Document attachment (ignore extra metadata like cache_control)
+    assert document_block["type"] == "document"
+    assert document_block["source"]["data"] == "ZmFrZV9pbWFnZV9kYXRh"
+    assert document_block["source"]["media_type"] == "application/pdf"
+    assert document_block["source"]["type"] == "base64"
diff --git a/tests/components/anthropic/test_conversation.py b/tests/components/anthropic/test_conversation.py
index ac54272fe0a..84a692335f1 100644
--- a/tests/components/anthropic/test_conversation.py
+++ b/tests/components/anthropic/test_conversation.py
@@ -153,10 +153,13 @@ async def test_template_variables(
         result.response.speech["plain"]["speech"]
         == "Okay, let me take care of that for you."
     )
-    assert (
-        "The user name is Test User." in mock_create_stream.call_args.kwargs["system"]
-    )
-    assert "The user id is 12345." in mock_create_stream.call_args.kwargs["system"]
+
+    system = mock_create_stream.call_args.kwargs["system"]
+    assert isinstance(system, list)
+    system_text = " ".join(block["text"] for block in system if "text" in block)
+
+    assert "The user name is Test User." in system_text
+    assert "The user id is 12345." in system_text
 
 
 async def test_conversation_agent(
@@ -169,6 +172,38 @@ async def test_conversation_agent(
     assert agent.supported_languages == "*"
 
 
+async def test_system_prompt_uses_text_block_with_cache_control(
+    hass: HomeAssistant,
+    mock_config_entry: MockConfigEntry,
+    mock_create_stream: AsyncMock,
+) -> None:
+    """Ensure system prompt is sent as TextBlockParam with cache_control."""
+    context = Context()
+
+    mock_create_stream.return_value = [
+        create_content_block(0, ["ok"]),
+    ]
+
+    with patch("anthropic.resources.models.AsyncModels.list", new_callable=AsyncMock):
+        await hass.config_entries.async_setup(mock_config_entry.entry_id)
+        await hass.async_block_till_done()
+        await conversation.async_converse(
+            hass,
+            "hello",
+            None,
+            context,
+            agent_id="conversation.claude_conversation",
+        )
+
+    system = mock_create_stream.call_args.kwargs["system"]
+    assert isinstance(system, list)
+    assert len(system) == 1
+    block = system[0]
+    assert block["type"] == "text"
+    assert "Home Assistant" in block["text"]
+    assert block["cache_control"] == {"type": "ephemeral"}
+
+
 @patch("homeassistant.components.anthropic.entity.llm.AssistAPI._async_get_tools")
 @pytest.mark.parametrize(
     ("tool_call_json_parts", "expected_call_tool_args"),
@@ -229,10 +264,10 @@ async def test_function_call(
             agent_id=agent_id,
         )
 
-    assert (
-        "You are a voice assistant for Home Assistant."
-        in mock_create_stream.mock_calls[1][2]["system"]
-    )
+    system = mock_create_stream.mock_calls[1][2]["system"]
+    assert isinstance(system, list)
+    system_text = " ".join(block["text"] for block in system if "text" in block)
+    assert "You are a voice assistant for Home Assistant." in system_text
 
     assert result.response.response_type == intent.IntentResponseType.ACTION_DONE
     assert (