diff --git a/cecli/mcp/server.py b/cecli/mcp/server.py
index c3758e76a55..bb3cf4fc279 100644
--- a/cecli/mcp/server.py
+++ b/cecli/mcp/server.py
@@ -337,7 +337,9 @@ async def _enter_client_session(self, read, write):
             ClientSession(
                 read,
                 write,
-                read_timeout_seconds=timedelta(seconds=self._request_timeout_seconds()),
+                read_timeout_seconds=_client_session_read_timeout(
+                    self._request_timeout_seconds()
+                ),
             )
         )
         await session.initialize()
@@ -732,3 +734,19 @@ def _unpack_transport(transport):
     """
     read, write = transport[0], transport[1]
     return read, write
+
+
+def _client_session_read_timeout(seconds: float) -> timedelta | float:
+    """Return a read timeout in the form the installed mcp SDK expects.
+
+    mcp SDK 1.x types ``ClientSession.read_timeout_seconds`` as a
+    ``timedelta``; SDK 2.x types it as a float number of seconds and adds it to
+    other floats internally, so a ``timedelta`` raises ``TypeError:
+    unsupported operand type(s) for +: 'float' and 'datetime.timedelta'`` at
+    connect time. Return whichever type the installed SDK wants, so both majors
+    keep the same per-request timeout instead of failing to connect.
+    """
+    if _get_mcp_major_version() >= 2:
+        return seconds
+
+    return timedelta(seconds=seconds)
diff --git a/tests/mcp/test_server_sdk_compat.py b/tests/mcp/test_server_sdk_compat.py
index abe7dcafe7f..1f274c99174 100644
--- a/tests/mcp/test_server_sdk_compat.py
+++ b/tests/mcp/test_server_sdk_compat.py
@@ -6,12 +6,14 @@
 static headers are configured).
 """
 
+from datetime import timedelta
 from unittest.mock import AsyncMock, MagicMock, patch
 
 import pytest
 
 from cecli.mcp.server import (
     HttpStreamingServer,
+    _client_session_read_timeout,
     _get_http_client_module,
     _get_mcp_major_version,
     _get_oauth_callback_handler,
@@ -77,6 +79,23 @@ def test_unpack_transport_mcp2_two_tuple(monkeypatch):
     assert (read, write) == ("r", "w")
 
 
+def test_client_session_read_timeout_timedelta_for_mcp1(monkeypatch):
+    """mcp 1.x types the session read timeout as a timedelta."""
+    monkeypatch.setattr("cecli.mcp.server._get_mcp_major_version", lambda: 1)
+
+    assert _client_session_read_timeout(120.0) == timedelta(seconds=120)
+
+
+def test_client_session_read_timeout_float_for_mcp2(monkeypatch):
+    """mcp 2.x types the session read timeout as a float number of seconds."""
+    monkeypatch.setattr("cecli.mcp.server._get_mcp_major_version", lambda: 2)
+
+    timeout = _client_session_read_timeout(120.0)
+
+    assert timeout == 120.0
+    assert not isinstance(timeout, timedelta)
+
+
 @pytest.mark.asyncio
 async def test_oauth_callback_handler_mcp1_passthrough(monkeypatch):
     """mcp 1.x uses the raw callback returning an (auth_code, state) tuple."""