Business Rules run server-side, so the correct APIs come from the GlideSystem object (gs) rather than client-side objects like g_form. In server-side scripting, the platform provides a standard way to retrieve the currently logged-in user’s identity. The method gs.getUserID() returns the sys_id of the user associated with the current session. This is commonly used in Business Rules for auditing logic, conditional processing, field stamping (for example, setting a custom “last processed by” field), or enforcing business rules based on user identity. The g_form object is a client-side API available in Client Scripts and UI Policies, so any option using g_form is invalid in a Business Rule context. Likewise, gs.getUserSysID() is not the documented method name for this purpose. Using the correct server-side API ensures the script executes reliably regardless of UI context (classic UI, workspace, mobile), because it relies on the session and not on the form rendering layer.