"While there was only one major acquisition announced during Xbox's E3 2019 press conference, Microsoft has one more new studio up its sleeve. In a blog post shared after the show, Microsoft snuck in that it has created a brand new studio for Age of Empires headed by Microsoft veteran Shannon Loftis. The news follows last night's announcement of Age of Empires II: Definitive Edition, which updates the classic strategy game with 4K visuals and a brand new campaign, The Last Khans. It will launch this autumn."
https://www.gamesindustry.biz/articles/2019-06-10-microsoft-forms-dedicated-age-of-empires-studio
So that's 15 studios under XGS. It's weird they did not announce it during their show but instead announced it through a blog post.