That'll be the sandbox adventure Core Keeper, while developer Brimstone has also revealed that rural city builder Overthrown is coming to the service via Xbox Game Preview in Fall 2024.
So, here's an introduction to these two upcoming Xbox Game Pass titles:
Core Keeper (Xbox Series X|S, PC) - August 27
"Explore an endless cavern of creatures, relics and resources in a mining sandbox adventure for 1-8 players. Mine, build, fight, craft and farm to unravel the mystery of the ancient Core."
Overthrown (Xbox Series X|S, PC) - Fall 2024
"Lift and throw anything as you build and manage your kingdom in this chaotic city builder for 1-6 players. Harness the power of your soul-stealing crown to defend your citizens from bandits and mutants, farm the land, and gather resources. Keep citizens happy or see them desert you!"