The ClientID is used for conflict resolution. So it is important that you understand all side-effects of retaining a ClientID across sessions. The simple answer is: Yjs is designed to create a new ClientID for every session to avoid sync conflicts. The recommended method to identify users is using the Awareness feature. If you still want to retain a ClientID, you can do so by simply overwriting the ydoc.clientID property. But you must ensure that no other Y.Doc instance is currently holding that ClientID. This is not always possible: A user might open several browser-windows with the same user account. When two Y.Doc instances with the same ClientID exist, the document might get permanently corrupted without a way to recover. So do this with caution.