Although Microsoft still has to make this official, multiple sources have confirmed that Xbox Game Pass Ultimate will be launched for US$14.99 and will combine the benefits that come with Xbox Game Pass and Xbox Live Gold. However, subscribing to these two services individually would cost US$5 more.
https://www.notebookcheck.net/Xbox-Game-Pass-Ultimate-to-join-Xbox-Live-Gold-and-Game-Pass-benefits-for-US-14-99-a-month-coming-soon.416020.0.html