diff --git a/openhands-sdk/openhands/sdk/conversation/impl/local_conversation.py b/openhands-sdk/openhands/sdk/conversation/impl/local_conversation.py
index 9113c4ecd9..c143003d2c 100644
--- a/openhands-sdk/openhands/sdk/conversation/impl/local_conversation.py
+++ b/openhands-sdk/openhands/sdk/conversation/impl/local_conversation.py
@@ -484,6 +484,17 @@ def _ensure_agent_ready(self) -> None:
 
             self._agent_ready = True
 
+    def _should_initialize_agent_on_send_message(self) -> bool:
+        """Return whether send_message() should eagerly initialize the agent.
+
+        ACPAgent startup is substantially heavier than regular agent
+        initialization because it launches and handshakes with an external ACP
+        subprocess. Deferring that work to run() keeps send_message() fast and
+        avoids HTTP client read timeouts on the remote conversation endpoint.
+        """
+        agent_kind = getattr(self.agent, "kind", self.agent.__class__.__name__)
+        return agent_kind != "ACPAgent"
+
     def switch_profile(self, profile_name: str) -> None:
         """Switch the agent's LLM to a named profile.
 
@@ -520,8 +531,12 @@ def send_message(self, message: str | Message, sender: str | None = None) -> Non
                    one agent delegates to another, the sender can be set to
                    identify which agent is sending the message.
         """
-        # Ensure agent is fully initialized (loads plugins and initializes agent)
-        self._ensure_agent_ready()
+        # ACPAgent startup can take much longer than a normal send_message()
+        # round-trip because it launches and initializes a subprocess-backed
+        # session. Defer that work to run() so enqueueing the user message
+        # remains fast for remote callers.
+        if self._should_initialize_agent_on_send_message():
+            self._ensure_agent_ready()
 
         if isinstance(message, str):
             message = Message(role="user", content=[TextContent(text=message)])
diff --git a/tests/sdk/conversation/local/test_conversation_send_message.py b/tests/sdk/conversation/local/test_conversation_send_message.py
index e19f87c334..aa46ef6a73 100644
--- a/tests/sdk/conversation/local/test_conversation_send_message.py
+++ b/tests/sdk/conversation/local/test_conversation_send_message.py
@@ -1,8 +1,14 @@
+from unittest.mock import patch
+
 from pydantic import SecretStr
 
+from openhands.sdk.agent.acp_agent import ACPAgent
 from openhands.sdk.agent.base import AgentBase
 from openhands.sdk.conversation import Conversation, LocalConversation
-from openhands.sdk.conversation.state import ConversationState
+from openhands.sdk.conversation.state import (
+    ConversationExecutionStatus,
+    ConversationState,
+)
 from openhands.sdk.conversation.types import (
     ConversationCallbackType,
     ConversationTokenCallbackType,
@@ -153,3 +159,35 @@ def test_send_message_with_message_object():
     assert len(user_event.llm_message.content) == 1
     assert isinstance(user_event.llm_message.content[0], TextContent)
     assert user_event.llm_message.content[0].text == test_text
+
+
+def test_acp_send_message_defers_initialization_until_run(tmp_path):
+    """ACP conversations should enqueue messages before starting ACP bootstrap."""
+
+    agent = ACPAgent(acp_command=["echo", "test"])
+    conversation = LocalConversation(agent=agent, workspace=str(tmp_path))
+
+    def _finish_immediately(self, conv, on_event, on_token=None):
+        conv.state.execution_status = ConversationExecutionStatus.FINISHED
+
+    with (
+        patch.object(ACPAgent, "init_state", autospec=True) as mock_init_state,
+        patch.object(
+            ACPAgent,
+            "step",
+            autospec=True,
+            side_effect=_finish_immediately,
+        ) as mock_step,
+    ):
+        conversation.send_message("Hello from ACP")
+
+        assert mock_init_state.call_count == 0
+        assert mock_step.call_count == 0
+        assert len(conversation.state.events) == 1
+        assert isinstance(conversation.state.events[-1], MessageEvent)
+        assert conversation.state.events[-1].source == "user"
+
+        conversation.run()
+
+        assert mock_init_state.call_count == 1
+        assert mock_step.call_count == 1