diff --git a/duckdb_engine/config.py b/duckdb_engine/config.py
index 41c279b02..353151df6 100644
--- a/duckdb_engine/config.py
+++ b/duckdb_engine/config.py
@@ -11,9 +11,20 @@
 
 @lru_cache()
 def get_core_config() -> Set[str]:
-    # List of connection string parameters that are supported by MotherDuck
-    # See: https://motherduck.com/docs/key-tasks/authenticating-and-connecting-to-motherduck/authenticating-to-motherduck/
-    motherduck_config_keys = {"motherduck_token", "attach_mode", "saas_mode"}
+    # MotherDuck settings that must be passed to duckdb.connect() as config:
+    # applying them via SET after the connection is established either fails
+    # with "can only be set during initialization" or happens too late. As
+    # duckdb settings they carry the motherduck_ prefix; the bare
+    # attach_mode/saas_mode spellings are only valid inside the md: path
+    # itself (e.g. "md:db?attach_mode=single") and were never recognized by
+    # duckdb.connect().
+    motherduck_config_keys = {
+        "motherduck_token",
+        "motherduck_attach_mode",
+        "motherduck_saas_mode",
+        "motherduck_session_name",
+        "motherduck_session_hint",  # deprecated alias of motherduck_session_name
+    }
 
     rows = (
         duckdb.connect(":memory:")
diff --git a/duckdb_engine/tests/test_basic.py b/duckdb_engine/tests/test_basic.py
index 15fda1fea..3df3aed94 100644
--- a/duckdb_engine/tests/test_basic.py
+++ b/duckdb_engine/tests/test_basic.py
@@ -40,6 +40,7 @@
 
 from .. import Dialect, insert, supports_attach, supports_user_agent
 from .._supports import has_comment_support
+from ..config import get_core_config
 
 try:
     # sqlalchemy 2
@@ -706,3 +707,17 @@ def test_register_filesystem() -> None:
     with engine.connect() as conn:
         duckdb_conn = getattr(conn.connection.dbapi_connection, "_ConnectionWrapper__c")
         assert duckdb.list_filesystems(connection=duckdb_conn) == ["memory", "file"]
+
+
+def test_motherduck_keys_are_connect_time_config() -> None:
+    core = get_core_config()
+    assert {
+        "motherduck_token",
+        "motherduck_attach_mode",
+        "motherduck_saas_mode",
+        "motherduck_session_name",
+        "motherduck_session_hint",
+    } <= core
+    # The bare spellings are md: path parameters, not duckdb settings.
+    assert "attach_mode" not in core
+    assert "saas_mode" not in core