diff --git a/libs/langchain_v1/langchain/agents/factory.py b/libs/langchain_v1/langchain/agents/factory.py
index eb07787929124..e221f9ac69eba 100644
--- a/libs/langchain_v1/langchain/agents/factory.py
+++ b/libs/langchain_v1/langchain/agents/factory.py
@@ -545,7 +545,7 @@ def create_agent(  # noqa: PLR0915
     model: str | BaseChatModel,
     tools: Sequence[BaseTool | Callable | dict[str, Any]] | None = None,
     *,
-    system_prompt: str | None = None,
+    system_prompt: str | SystemMessage | None = None,
     middleware: Sequence[AgentMiddleware[StateT_co, ContextT]] = (),
     response_format: ResponseFormat[ResponseT] | type[ResponseT] | None = None,
     state_schema: type[AgentState[ResponseT]] | None = None,
@@ -591,9 +591,9 @@ def create_agent(  # noqa: PLR0915
                 docs for more information.
         system_prompt: An optional system prompt for the LLM.
 
-            Prompts are converted to a
-            [`SystemMessage`][langchain.messages.SystemMessage] and added to the
-            beginning of the message list.
+            Can be a `str` (which will be converted to a `SystemMessage`) or a
+            `SystemMessage` instance directly. The system message is added to the
+            beginning of the message list when calling the model.
         middleware: A sequence of middleware instances to apply to the agent.
 
             Middleware can intercept and modify agent behavior at various stages.
@@ -688,6 +688,14 @@ def check_weather(location: str) -> str:
     if isinstance(model, str):
         model = init_chat_model(model)
 
+    # Convert system_prompt to SystemMessage if needed
+    system_message: SystemMessage | None = None
+    if system_prompt is not None:
+        if isinstance(system_prompt, SystemMessage):
+            system_message = system_prompt
+        else:
+            system_message = SystemMessage(content=system_prompt)
+
     # Handle tools being None or empty
     if tools is None:
         tools = []
@@ -1091,8 +1099,8 @@ def _execute_model_sync(request: ModelRequest) -> ModelResponse:
         # Get the bound model (with auto-detection if needed)
         model_, effective_response_format = _get_bound_model(request)
         messages = request.messages
-        if request.system_prompt:
-            messages = [SystemMessage(request.system_prompt), *messages]
+        if request.system_message:
+            messages = [request.system_message, *messages]
 
         output = model_.invoke(messages)
 
@@ -1111,7 +1119,7 @@ def model_node(state: AgentState, runtime: Runtime[ContextT]) -> dict[str, Any]:
         request = ModelRequest(
             model=model,
             tools=default_tools,
-            system_prompt=system_prompt,
+            system_message=system_message,
             response_format=initial_response_format,
             messages=state["messages"],
             tool_choice=None,
@@ -1144,8 +1152,8 @@ async def _execute_model_async(request: ModelRequest) -> ModelResponse:
         # Get the bound model (with auto-detection if needed)
         model_, effective_response_format = _get_bound_model(request)
         messages = request.messages
-        if request.system_prompt:
-            messages = [SystemMessage(request.system_prompt), *messages]
+        if request.system_message:
+            messages = [request.system_message, *messages]
 
         output = await model_.ainvoke(messages)
 
@@ -1164,7 +1172,7 @@ async def amodel_node(state: AgentState, runtime: Runtime[ContextT]) -> dict[str
         request = ModelRequest(
             model=model,
             tools=default_tools,
-            system_prompt=system_prompt,
+            system_message=system_message,
             response_format=initial_response_format,
             messages=state["messages"],
             tool_choice=None,
diff --git a/libs/langchain_v1/langchain/agents/middleware/context_editing.py b/libs/langchain_v1/langchain/agents/middleware/context_editing.py
index 42488276abda3..538b6ee56766e 100644
--- a/libs/langchain_v1/langchain/agents/middleware/context_editing.py
+++ b/libs/langchain_v1/langchain/agents/middleware/context_editing.py
@@ -18,7 +18,6 @@
     AIMessage,
     AnyMessage,
     BaseMessage,
-    SystemMessage,
     ToolMessage,
 )
 from langchain_core.messages.utils import count_tokens_approximately
@@ -230,9 +229,7 @@ def wrap_model_call(
             def count_tokens(messages: Sequence[BaseMessage]) -> int:
                 return count_tokens_approximately(messages)
         else:
-            system_msg = (
-                [SystemMessage(content=request.system_prompt)] if request.system_prompt else []
-            )
+            system_msg = [request.system_message] if request.system_message else []
 
             def count_tokens(messages: Sequence[BaseMessage]) -> int:
                 return request.model.get_num_tokens_from_messages(
@@ -259,9 +256,7 @@ async def awrap_model_call(
             def count_tokens(messages: Sequence[BaseMessage]) -> int:
                 return count_tokens_approximately(messages)
         else:
-            system_msg = (
-                [SystemMessage(content=request.system_prompt)] if request.system_prompt else []
-            )
+            system_msg = [request.system_message] if request.system_message else []
 
             def count_tokens(messages: Sequence[BaseMessage]) -> int:
                 return request.model.get_num_tokens_from_messages(
diff --git a/libs/langchain_v1/langchain/agents/middleware/todo.py b/libs/langchain_v1/langchain/agents/middleware/todo.py
index ac5bfbee0881e..ce70de42cab48 100644
--- a/libs/langchain_v1/langchain/agents/middleware/todo.py
+++ b/libs/langchain_v1/langchain/agents/middleware/todo.py
@@ -8,7 +8,7 @@
 if TYPE_CHECKING:
     from collections.abc import Awaitable, Callable
 
-from langchain_core.messages import ToolMessage
+from langchain_core.messages import SystemMessage, ToolMessage
 from langchain_core.tools import tool
 from langgraph.types import Command
 from typing_extensions import NotRequired, TypedDict
@@ -193,23 +193,25 @@ def wrap_model_call(
         request: ModelRequest,
         handler: Callable[[ModelRequest], ModelResponse],
     ) -> ModelCallResult:
-        """Update the system prompt to include the todo system prompt."""
-        new_system_prompt = (
-            request.system_prompt + "\n\n" + self.system_prompt
-            if request.system_prompt
+        """Update the system message to include the todo system prompt."""
+        new_system_content = (
+            request.system_message.content + "\n\n" + self.system_prompt
+            if request.system_message
             else self.system_prompt
         )
-        return handler(request.override(system_prompt=new_system_prompt))
+        new_system_message = SystemMessage(content=new_system_content)
+        return handler(request.override(system_message=new_system_message))
 
     async def awrap_model_call(
         self,
         request: ModelRequest,
         handler: Callable[[ModelRequest], Awaitable[ModelResponse]],
     ) -> ModelCallResult:
-        """Update the system prompt to include the todo system prompt (async version)."""
-        new_system_prompt = (
-            request.system_prompt + "\n\n" + self.system_prompt
-            if request.system_prompt
+        """Update the system message to include the todo system prompt (async version)."""
+        new_system_content = (
+            request.system_message.content + "\n\n" + self.system_prompt
+            if request.system_message
             else self.system_prompt
         )
-        return await handler(request.override(system_prompt=new_system_prompt))
+        new_system_message = SystemMessage(content=new_system_content)
+        return await handler(request.override(system_message=new_system_message))
diff --git a/libs/langchain_v1/langchain/agents/middleware/types.py b/libs/langchain_v1/langchain/agents/middleware/types.py
index 998fec8571655..5e8574620e2e4 100644
--- a/libs/langchain_v1/langchain/agents/middleware/types.py
+++ b/libs/langchain_v1/langchain/agents/middleware/types.py
@@ -20,12 +20,14 @@
     from collections.abc import Awaitable
 
 # Needed as top level import for Pydantic schema generation on AgentState
+import warnings
 from typing import TypeAlias
 
-from langchain_core.messages import (  # noqa: TC002
+from langchain_core.messages import (
     AIMessage,
     AnyMessage,
     BaseMessage,
+    SystemMessage,
     ToolMessage,
 )
 from langgraph.channels.ephemeral_value import EphemeralValue
@@ -72,7 +74,7 @@ class _ModelRequestOverrides(TypedDict, total=False):
     """Possible overrides for `ModelRequest.override()` method."""
 
     model: BaseChatModel
-    system_prompt: str | None
+    system_message: SystemMessage | None
     messages: list[AnyMessage]
     tool_choice: Any | None
     tools: list[BaseTool | dict]
@@ -80,13 +82,13 @@ class _ModelRequestOverrides(TypedDict, total=False):
     model_settings: dict[str, Any]
 
 
-@dataclass
+@dataclass(init=False)
 class ModelRequest:
     """Model request information for the agent."""
 
     model: BaseChatModel
-    system_prompt: str | None
-    messages: list[AnyMessage]  # excluding system prompt
+    messages: list[AnyMessage]  # excluding system message
+    system_message: SystemMessage | None
     tool_choice: Any | None
     tools: list[BaseTool | dict]
     response_format: ResponseFormat | None
@@ -94,6 +96,65 @@ class ModelRequest:
     runtime: Runtime[ContextT]  # type: ignore[valid-type]
     model_settings: dict[str, Any] = field(default_factory=dict)
 
+    def __init__(
+        self,
+        *,
+        model: BaseChatModel,
+        messages: list[AnyMessage],
+        system_message: SystemMessage | None = None,
+        system_prompt: str | None = None,
+        tool_choice: Any | None = None,
+        tools: list[BaseTool | dict] | None = None,
+        response_format: ResponseFormat | None = None,
+        state: AgentState | None = None,
+        runtime: Runtime[ContextT] | None = None,
+        model_settings: dict[str, Any] | None = None,
+    ) -> None:
+        """Initialize ModelRequest with backward compatibility for system_prompt.
+
+        Args:
+            model: The chat model to use.
+            messages: List of messages (excluding system prompt).
+            tool_choice: Tool choice configuration.
+            tools: List of available tools.
+            response_format: Response format specification.
+            state: Agent state.
+            runtime: Runtime context.
+            model_settings: Additional model settings.
+            system_message: System message instance (preferred).
+            system_prompt: System prompt string (deprecated, converted to SystemMessage).
+        """
+        # Handle system_prompt/system_message conversion and validation
+        if system_prompt is not None and system_message is not None:
+            msg = "Cannot specify both system_prompt and system_message"
+            raise ValueError(msg)
+
+        if system_prompt is not None:
+            system_message = SystemMessage(content=system_prompt)
+
+        with warnings.catch_warnings():
+            warnings.simplefilter("ignore", category=DeprecationWarning)
+            self.model = model
+            self.messages = messages
+            self.system_message = system_message
+            self.tool_choice = tool_choice
+            self.tools = tools if tools is not None else []
+            self.response_format = response_format
+            self.state = state if state is not None else {"messages": []}
+            self.runtime = runtime  # type: ignore[assignment]
+            self.model_settings = model_settings if model_settings is not None else {}
+
+    @property
+    def system_prompt(self) -> str | None:
+        """Get system prompt text from system_message.
+
+        Returns:
+            The content of the system message if present, otherwise `None`.
+        """
+        if self.system_message is None:
+            return None
+        return self.system_message.text
+
     def __setattr__(self, name: str, value: Any) -> None:
         """Set an attribute with a deprecation warning.
 
@@ -104,20 +165,29 @@ def __setattr__(self, name: str, value: Any) -> None:
             name: Attribute name.
             value: Attribute value.
         """
-        import warnings
-
-        # Allow setting attributes during __init__ (when object is being constructed)
-        if not hasattr(self, "__dataclass_fields__") or not hasattr(self, name):
-            object.__setattr__(self, name, value)
-        else:
+        # Special handling for system_prompt - convert to system_message
+        if name == "system_prompt":
             warnings.warn(
-                f"Direct attribute assignment to ModelRequest.{name} is deprecated. "
-                f"Use request.override({name}=...) instead to create a new request "
-                f"with the modified attribute.",
+                "Direct attribute assignment to ModelRequest.system_prompt is deprecated. "
+                "Use request.override(system_message=SystemMessage(...)) instead to create "
+                "a new request with the modified system message.",
                 DeprecationWarning,
                 stacklevel=2,
             )
-            object.__setattr__(self, name, value)
+            if value is None:
+                object.__setattr__(self, "system_message", None)
+            else:
+                object.__setattr__(self, "system_message", SystemMessage(content=value))
+            return
+
+        warnings.warn(
+            f"Direct attribute assignment to ModelRequest.{name} is deprecated. "
+            f"Use request.override({name}=...) instead to create a new request "
+            f"with the modified attribute.",
+            DeprecationWarning,
+            stacklevel=2,
+        )
+        object.__setattr__(self, name, value)
 
     def override(self, **overrides: Unpack[_ModelRequestOverrides]) -> ModelRequest:
         """Replace the request with a new request with the given overrides.
@@ -132,7 +202,8 @@ def override(self, **overrides: Unpack[_ModelRequestOverrides]) -> ModelRequest:
                 Supported keys:
 
                 - `model`: `BaseChatModel` instance
-                - `system_prompt`: Optional system prompt string
+                - `system_prompt`: deprecated, use `system_message` instead
+                - `system_message`: `SystemMessage` instance
                 - `messages`: `list` of messages
                 - `tool_choice`: Tool choice configuration
                 - `tools`: `list` of available tools
@@ -149,12 +220,36 @@ def override(self, **overrides: Unpack[_ModelRequestOverrides]) -> ModelRequest:
                 new_request = request.override(model=different_model)
                 ```
 
-            !!! example "Override multiple attributes"
+            !!! example "Override system message (preferred)"
 
                 ```python
-                new_request = request.override(system_prompt="New instructions", tool_choice="auto")
+                from langchain_core.messages import SystemMessage
+
+                new_request = request.override(
+                    system_message=SystemMessage(content="New instructions")
+                )
+                ```
+
+            !!! example "Override system prompt (backward compatible)"
+
+                ```python
+                new_request = request.override(system_prompt="New instructions")
                 ```
         """
+        # Handle system_prompt/system_message conversion
+        if "system_prompt" in overrides and "system_message" in overrides:
+            msg = "Cannot specify both system_prompt and system_message"
+            raise ValueError(msg)
+
+        if "system_prompt" in overrides:
+            system_prompt = overrides["system_prompt"]
+            if system_prompt is None:
+                overrides["system_message"] = None
+            else:
+                overrides["system_message"] = SystemMessage(content=system_prompt)
+            # Remove system_prompt from overrides to avoid conflict
+            overrides = {k: v for k, v in overrides.items() if k != "system_prompt"}
+
         return replace(self, **overrides)
 
 
@@ -603,10 +698,12 @@ def __call__(
 
 
 class _CallableReturningPromptString(Protocol[StateT_contra, ContextT]):  # type: ignore[misc]
-    """Callable that returns a prompt string given `ModelRequest` (contains state and runtime)."""
+    """Callable that returns a prompt string or SystemMessage given `ModelRequest`."""
 
-    def __call__(self, request: ModelRequest) -> str | Awaitable[str]:
-        """Generate a system prompt string based on the request."""
+    def __call__(
+        self, request: ModelRequest
+    ) -> str | SystemMessage | Awaitable[str | SystemMessage]:
+        """Generate a system prompt string or SystemMessage based on the request."""
         ...
 
 
@@ -1326,7 +1423,8 @@ def dynamic_prompt(
             function that can be applied to a function.
 
     The decorated function should return:
-        - `str` – The system prompt to use for the model request
+        - `str` – The system prompt string to use for the model request
+        - `SystemMessage` – A complete system message to use for the model request
 
     Examples:
         Basic usage with dynamic content:
@@ -1369,7 +1467,10 @@ async def async_wrapped(
                 handler: Callable[[ModelRequest], Awaitable[ModelResponse]],
             ) -> ModelCallResult:
                 prompt = await func(request)  # type: ignore[misc]
-                request = request.override(system_prompt=prompt)
+                if isinstance(prompt, SystemMessage):
+                    request = request.override(system_message=prompt)
+                else:
+                    request = request.override(system_message=SystemMessage(content=prompt))
                 return await handler(request)
 
             middleware_name = cast("str", getattr(func, "__name__", "DynamicPromptMiddleware"))
@@ -1389,8 +1490,11 @@ def wrapped(
             request: ModelRequest,
             handler: Callable[[ModelRequest], ModelResponse],
         ) -> ModelCallResult:
-            prompt = cast("str", func(request))
-            request = request.override(system_prompt=prompt)
+            prompt = func(request)
+            if isinstance(prompt, SystemMessage):
+                request = request.override(system_message=prompt)
+            else:
+                request = request.override(system_message=SystemMessage(content=prompt))
             return handler(request)
 
         async def async_wrapped_from_sync(
@@ -1399,8 +1503,11 @@ async def async_wrapped_from_sync(
             handler: Callable[[ModelRequest], Awaitable[ModelResponse]],
         ) -> ModelCallResult:
             # Delegate to sync function
-            prompt = cast("str", func(request))
-            request = request.override(system_prompt=prompt)
+            prompt = func(request)
+            if isinstance(prompt, SystemMessage):
+                request = request.override(system_message=prompt)
+            else:
+                request = request.override(system_message=SystemMessage(content=prompt))
             return await handler(request)
 
         middleware_name = cast("str", getattr(func, "__name__", "DynamicPromptMiddleware"))
diff --git a/libs/langchain_v1/tests/unit_tests/agents/test_system_message_support.py b/libs/langchain_v1/tests/unit_tests/agents/test_system_message_support.py
new file mode 100644
index 0000000000000..d56696b370b4f
--- /dev/null
+++ b/libs/langchain_v1/tests/unit_tests/agents/test_system_message_support.py
@@ -0,0 +1,263 @@
+"""Unit tests for SystemMessage support in create_agent and ModelRequest."""
+
+import pytest
+from langchain_core.language_models.fake_chat_models import GenericFakeChatModel
+from langchain_core.messages import AIMessage, HumanMessage, SystemMessage
+
+from langchain.agents.middleware.types import ModelRequest
+
+
+class TestModelRequestSystemMessage:
+    """Test ModelRequest with system_message field."""
+
+    def test_create_with_system_message(self) -> None:
+        """Test creating ModelRequest with SystemMessage."""
+        model = GenericFakeChatModel(messages=iter([AIMessage(content="Hello")]))
+        system_msg = SystemMessage(content="You are a helpful assistant")
+
+        request = ModelRequest(
+            model=model,
+            system_message=system_msg,
+            messages=[HumanMessage("Hi")],
+            tool_choice=None,
+            tools=[],
+            response_format=None,
+            state={},
+            runtime=None,
+        )
+
+        assert request.system_message == system_msg
+        assert request.system_prompt == "You are a helpful assistant"
+
+    def test_create_with_none_system_message(self) -> None:
+        """Test creating ModelRequest with None system_message."""
+        model = GenericFakeChatModel(messages=iter([AIMessage(content="Hello")]))
+
+        request = ModelRequest(
+            model=model,
+            system_message=None,
+            messages=[HumanMessage("Hi")],
+            tool_choice=None,
+            tools=[],
+            response_format=None,
+            state={},
+            runtime=None,
+        )
+
+        assert request.system_message is None
+        assert request.system_prompt is None
+
+    def test_system_prompt_property_with_string_content(self) -> None:
+        """Test system_prompt property returns content from SystemMessage."""
+        model = GenericFakeChatModel(messages=iter([AIMessage(content="Hello")]))
+        system_msg = SystemMessage(content="Test prompt")
+
+        request = ModelRequest(
+            model=model,
+            system_message=system_msg,
+            messages=[],
+            tool_choice=None,
+            tools=[],
+            response_format=None,
+            state={},
+            runtime=None,
+        )
+
+        assert request.system_prompt == "Test prompt"
+
+    def test_system_prompt_property_with_list_content(self) -> None:
+        """Test system_prompt property handles list content."""
+        model = GenericFakeChatModel(messages=iter([AIMessage(content="Hello")]))
+        system_msg = SystemMessage(content=["Part 1", "Part 2"])
+
+        request = ModelRequest(
+            model=model,
+            system_message=system_msg,
+            messages=[],
+            tool_choice=None,
+            tools=[],
+            response_format=None,
+            state={},
+            runtime=None,
+        )
+
+        # Should convert list content to string
+        assert request.system_prompt is not None
+        assert "Part 1" in request.system_prompt
+
+    def test_override_with_system_message(self) -> None:
+        """Test override() with system_message parameter."""
+        model = GenericFakeChatModel(messages=iter([AIMessage(content="Hello")]))
+        original_msg = SystemMessage(content="Original")
+        new_msg = SystemMessage(content="New")
+
+        original_request = ModelRequest(
+            model=model,
+            system_message=original_msg,
+            messages=[],
+            tool_choice=None,
+            tools=[],
+            response_format=None,
+            state={},
+            runtime=None,
+        )
+
+        new_request = original_request.override(system_message=new_msg)
+
+        assert new_request.system_message == new_msg
+        assert new_request.system_prompt == "New"
+        assert original_request.system_message == original_msg
+        assert original_request.system_prompt == "Original"
+
+    def test_override_with_system_prompt_backward_compat(self) -> None:
+        """Test override() with system_prompt parameter (backward compatibility)."""
+        model = GenericFakeChatModel(messages=iter([AIMessage(content="Hello")]))
+
+        original_request = ModelRequest(
+            model=model,
+            system_message=SystemMessage(content="Original"),
+            messages=[],
+            tool_choice=None,
+            tools=[],
+            response_format=None,
+            state={},
+            runtime=None,
+        )
+
+        # Override using system_prompt (backward compat)
+        new_request = original_request.override(system_prompt="New prompt")
+
+        assert new_request.system_prompt == "New prompt"
+        assert isinstance(new_request.system_message, SystemMessage)
+        assert new_request.system_message.content == "New prompt"
+
+    def test_override_system_prompt_to_none(self) -> None:
+        """Test override() setting system_prompt to None."""
+        model = GenericFakeChatModel(messages=iter([AIMessage(content="Hello")]))
+
+        original_request = ModelRequest(
+            model=model,
+            system_message=SystemMessage(content="Original"),
+            messages=[],
+            tool_choice=None,
+            tools=[],
+            response_format=None,
+            state={},
+            runtime=None,
+        )
+
+        new_request = original_request.override(system_prompt=None)
+
+        assert new_request.system_message is None
+        assert new_request.system_prompt is None
+
+    def test_setattr_system_prompt_deprecated(self) -> None:
+        """Test that setting system_prompt via setattr raises deprecation warning."""
+        model = GenericFakeChatModel(messages=iter([AIMessage(content="Hello")]))
+
+        request = ModelRequest(
+            model=model,
+            system_message=None,
+            messages=[],
+            tool_choice=None,
+            tools=[],
+            response_format=None,
+            state={},
+            runtime=None,
+        )
+
+        with pytest.warns(DeprecationWarning, match="system_prompt is deprecated"):
+            request.system_prompt = "New prompt"
+
+        # Should still work but convert to SystemMessage
+        assert isinstance(request.system_message, SystemMessage)
+        assert request.system_message.content == "New prompt"
+
+    def test_multiple_overrides_with_system_message(self) -> None:
+        """Test chaining overrides with system_message."""
+        model = GenericFakeChatModel(messages=iter([AIMessage(content="Hello")]))
+
+        original_request = ModelRequest(
+            model=model,
+            system_message=SystemMessage(content="Prompt 1"),
+            messages=[],
+            tool_choice=None,
+            tools=[],
+            response_format=None,
+            state={},
+            runtime=None,
+        )
+
+        final_request = (
+            original_request.override(system_message=SystemMessage(content="Prompt 2"))
+            .override(tool_choice="auto")
+            .override(system_message=SystemMessage(content="Prompt 3"))
+        )
+
+        assert final_request.system_prompt == "Prompt 3"
+        assert final_request.tool_choice == "auto"
+        assert original_request.system_prompt == "Prompt 1"
+
+
+class TestCreateAgentSystemMessage:
+    """Test create_agent with SystemMessage support."""
+
+    def test_create_agent_with_string_system_prompt(self) -> None:
+        """Test create_agent accepts string system_prompt (backward compat)."""
+        from langchain.agents import create_agent
+
+        model = GenericFakeChatModel(messages=iter([AIMessage(content="Hello")]))
+
+        # Should not raise - backward compatibility
+        agent = create_agent(
+            model=model,
+            system_prompt="You are a helpful assistant",
+        )
+
+        assert agent is not None
+
+    def test_create_agent_with_system_message(self) -> None:
+        """Test create_agent accepts SystemMessage for system_prompt."""
+        from langchain.agents import create_agent
+
+        model = GenericFakeChatModel(messages=iter([AIMessage(content="Hello")]))
+        system_msg = SystemMessage(content="You are a helpful assistant")
+
+        # Should not raise
+        agent = create_agent(
+            model=model,
+            system_prompt=system_msg,
+        )
+
+        assert agent is not None
+
+    def test_create_agent_with_none_system_prompt(self) -> None:
+        """Test create_agent with None system_prompt."""
+        from langchain.agents import create_agent
+
+        model = GenericFakeChatModel(messages=iter([AIMessage(content="Hello")]))
+
+        # Should not raise
+        agent = create_agent(
+            model=model,
+            system_prompt=None,
+        )
+
+        assert agent is not None
+
+    def test_create_agent_system_message_with_metadata(self) -> None:
+        """Test create_agent with SystemMessage containing metadata."""
+        from langchain.agents import create_agent
+
+        model = GenericFakeChatModel(messages=iter([AIMessage(content="Hello")]))
+        system_msg = SystemMessage(
+            content="You are a helpful assistant", additional_kwargs={"role": "system_admin"}
+        )
+
+        # Should not raise and preserve metadata
+        agent = create_agent(
+            model=model,
+            system_prompt=system_msg,
+        )
+
+        assert agent is not None