diff --git a/python/packages/autogen-agentchat/src/autogen_agentchat/agents/_assistant_agent.py b/python/packages/autogen-agentchat/src/autogen_agentchat/agents/_assistant_agent.py
index f60a44dbb90..a1acf8f6f8e 100644
--- a/python/packages/autogen-agentchat/src/autogen_agentchat/agents/_assistant_agent.py
+++ b/python/packages/autogen-agentchat/src/autogen_agentchat/agents/_assistant_agent.py
@@ -24,6 +24,7 @@
     FunctionExecutionResult,
     FunctionExecutionResultMessage,
     SystemMessage,
+    DeveloperMessage,
     UserMessage,
 )
 from autogen_core.tools import FunctionTool, Tool
@@ -238,15 +239,20 @@ def __init__(
         system_message: (
             str | None
         ) = "You are a helpful AI assistant. Solve tasks using your tools. Reply with TERMINATE when the task has been completed.",
+        developer_message: (str | None) = None,
         reflect_on_tool_use: bool = False,
         tool_call_summary_format: str = "{result}",
     ):
         super().__init__(name=name, description=description)
         self._model_client = model_client
-        if system_message is None:
+        if system_message is None or developer_message is not None:
             self._system_messages = []
         else:
             self._system_messages = [SystemMessage(content=system_message)]
+        if developer_message is None:
+            self._developer_messages = []
+        else:
+            self._developer_messages = [DeveloperMessage(content=developer_message)]
         self._tools: List[Tool] = []
         if tools is not None:
             if model_client.model_info["function_calling"] is False:
@@ -326,7 +332,10 @@ async def on_messages_stream(
         inner_messages: List[AgentEvent | ChatMessage] = []
 
         # Generate an inference result based on the current model context.
-        llm_messages = self._system_messages + await self._model_context.get_messages()
+        if len(self._developer_messages) > 0:
+            llm_messages = self._developer_messages + await self._model_context.get_messages()
+        else:
+            llm_messages = self._system_messages + await self._model_context.get_messages()
         result = await self._model_client.create(
             llm_messages, tools=self._tools + self._handoff_tools, cancellation_token=cancellation_token
         )
@@ -379,7 +388,10 @@ async def on_messages_stream(
 
         if self._reflect_on_tool_use:
             # Generate another inference result based on the tool call and result.
-            llm_messages = self._system_messages + await self._model_context.get_messages()
+            if len(self._developer_messages) > 0:
+                llm_messages = self._developer_messages + await self._model_context.get_messages()
+            else:
+                llm_messages = self._system_messages + await self._model_context.get_messages()
             result = await self._model_client.create(llm_messages, cancellation_token=cancellation_token)
             assert isinstance(result.content, str)
             # Add the response to the model context.
diff --git a/python/packages/autogen-core/src/autogen_core/models/__init__.py b/python/packages/autogen-core/src/autogen_core/models/__init__.py
index c9fa23ffa11..fbdfb2f22a4 100644
--- a/python/packages/autogen-core/src/autogen_core/models/__init__.py
+++ b/python/packages/autogen-core/src/autogen_core/models/__init__.py
@@ -9,6 +9,7 @@
     LLMMessage,
     RequestUsage,
     SystemMessage,
+    DeveloperMessage,
     TopLogprob,
     UserMessage,
 )
@@ -17,6 +18,7 @@
     "ModelCapabilities",
     "ChatCompletionClient",
     "SystemMessage",
+    "DeveloperMessage",
     "UserMessage",
     "AssistantMessage",
     "FunctionExecutionResult",
diff --git a/python/packages/autogen-core/src/autogen_core/models/_types.py b/python/packages/autogen-core/src/autogen_core/models/_types.py
index fb118562e4d..9f8b189017d 100644
--- a/python/packages/autogen-core/src/autogen_core/models/_types.py
+++ b/python/packages/autogen-core/src/autogen_core/models/_types.py
@@ -12,6 +12,11 @@ class SystemMessage(BaseModel):
     type: Literal["SystemMessage"] = "SystemMessage"
 
 
+class DeveloperMessage(BaseModel):
+    content: str
+    type: Literal["DeveloperMessage"] = "DeveloperMessage"
+
+
 class UserMessage(BaseModel):
     content: Union[str, List[Union[str, Image]]]
 
@@ -42,7 +47,8 @@ class FunctionExecutionResultMessage(BaseModel):
 
 
 LLMMessage = Annotated[
-    Union[SystemMessage, UserMessage, AssistantMessage, FunctionExecutionResultMessage], Field(discriminator="type")
+    Union[SystemMessage, DeveloperMessage, UserMessage, AssistantMessage, FunctionExecutionResultMessage],
+    Field(discriminator="type"),
 ]
 
 
diff --git a/python/packages/autogen-ext/src/autogen_ext/models/openai/_openai_client.py b/python/packages/autogen-ext/src/autogen_ext/models/openai/_openai_client.py
index 0a811dacce8..3f96950459c 100644
--- a/python/packages/autogen-ext/src/autogen_ext/models/openai/_openai_client.py
+++ b/python/packages/autogen-ext/src/autogen_ext/models/openai/_openai_client.py
@@ -43,6 +43,7 @@
     ModelInfo,
     RequestUsage,
     SystemMessage,
+    DeveloperMessage,
     TopLogprob,
     UserMessage,
 )
@@ -58,6 +59,7 @@
     ChatCompletionMessageToolCallParam,
     ChatCompletionRole,
     ChatCompletionSystemMessageParam,
+    ChatCompletionDeveloperMessageParam,
     ChatCompletionToolMessageParam,
     ChatCompletionToolParam,
     ChatCompletionUserMessageParam,
@@ -172,6 +174,13 @@ def system_message_to_oai(message: SystemMessage) -> ChatCompletionSystemMessage
     )
 
 
+def developer_message_to_oai(message: DeveloperMessage) -> ChatCompletionDeveloperMessageParam:
+    return ChatCompletionDeveloperMessageParam(
+        content=message.content,
+        role="developer",
+    )
+
+
 def func_call_to_oai(message: FunctionCall) -> ChatCompletionMessageToolCallParam:
     return ChatCompletionMessageToolCallParam(
         id=message.id,
@@ -212,6 +221,8 @@ def assistant_message_to_oai(
 def to_oai_type(message: LLMMessage) -> Sequence[ChatCompletionMessageParam]:
     if isinstance(message, SystemMessage):
         return [system_message_to_oai(message)]
+    elif isinstance(message, DeveloperMessage):
+        return [developer_message_to_oai(message)]
     elif isinstance(message, UserMessage):
         return [user_message_to_oai(message)]
     elif isinstance(message, AssistantMessage):