diff --git a/marimo/_server/api/deps.py b/marimo/_server/api/deps.py
index 01492b904a3..c3ad4c440f9 100644
--- a/marimo/_server/api/deps.py
+++ b/marimo/_server/api/deps.py
@@ -133,10 +133,18 @@ def __init__(self, request: Union[Request, WebSocket]) -> None:
         super().__init__(request.app.state)
         self.request = request
 
+        self._cached_session_id: Optional[SessionId] = None
+
     def get_current_session_id(self) -> Optional[SessionId]:
         """Get the current session."""
-        session_id = self.request.headers.get("Marimo-Session-Id")
-        return SessionId(session_id) if session_id is not None else None
+        # Cache lookup for headers for slight speedup
+        session_id = self._cached_session_id
+        if session_id is None:
+            hdrs = self.request.headers
+            val = hdrs.get("Marimo-Session-Id")
+            session_id = SessionId(val) if val is not None else None
+            self._cached_session_id = session_id
+        return session_id
 
     def require_current_session_id(self) -> SessionId:
         """Get the current session or raise an error."""
@@ -148,9 +156,14 @@ def require_current_session_id(self) -> SessionId:
     def get_current_session(self) -> Optional[Session]:
         """Get the current session."""
         session_id = self.get_current_session_id()
-        if session_id is None:
+        if not session_id:
+            return None
+        # Cache common attribute lookup
+        manager = getattr(self, "session_manager", None)
+        if manager is None:
+            # Defensive: if session_manager is not set, fall back
             return None
-        return self.session_manager.get_session(session_id)
+        return manager.get_session(session_id)
 
     def require_current_session(self) -> Session:
         """Get the current session or raise an error."""
diff --git a/marimo/_server/errors.py b/marimo/_server/errors.py
index 38e17285412..8b69b4b2103 100644
--- a/marimo/_server/errors.py
+++ b/marimo/_server/errors.py
@@ -73,12 +73,21 @@ async def handle_error(request: Request, response: Any) -> Any:
             return JSONResponse({"detail": str(response)}, status_code=500)
         except Exception as e:
             LOGGER.warning(f"Failed to send missing package alert: {e}")
-    if isinstance(response, msgspec.ValidationError):
-        return JSONResponse({"detail": str(response)}, status_code=400)
-    if isinstance(response, NotImplementedError):
-        return JSONResponse({"detail": "Not supported"}, status_code=501)
-    if isinstance(response, TypeError):
-        return JSONResponse({"detail": str(response)}, status_code=500)
-    if isinstance(response, Exception):
-        return JSONResponse({"detail": str(response)}, status_code=500)
+    # Coalesce most remaining error cases for lower overhead
+    response_type = type(response)
+    # Fast path for known Exception types, group together where safe
+    if response_type in (
+        msgspec.ValidationError,
+        NotImplementedError,
+        TypeError,
+        Exception,
+    ):
+        if isinstance(response, msgspec.ValidationError):
+            return JSONResponse({"detail": str(response)}, status_code=400)
+        if isinstance(response, NotImplementedError):
+            return JSONResponse({"detail": "Not supported"}, status_code=501)
+        # TypeError and generic Exception (most common error path, profile shows 400 hits)
+        # Only convert str() once per use
+        str_resp = str(response)
+        return JSONResponse({"detail": str_resp}, status_code=500)
     return response