In fact, the company explicitly promised that its own in-house, first-party games won't require you to buy the new Series X console for two years. Here's Xbox boss Phil Spencer
just last week:
You won't be forced into the next generation. We want every Xbox player to play all the new games from Xbox Game Studios. That's why Xbox Game Studios titles we release in the next couple of years—like Halo Infinite—will be available and play great on Xbox Series X and Xbox One. We won't force you to upgrade to Xbox Series X at launch to play Xbox exclusives."
And here's what Xbox Game Studios head Matt Booty
told MCV in January (bolding ours):
"As our content comes out over the next year, two years, all of our games, sort of like PC, will play up and down that family of devices," Booty explains. "We want to make sure that if someone invests in Xbox between now and [Series X] that they feel that they made a good investment and that we're committed to them with content."
Heck, here's a third version of the promise
from March, again with additional bolding:
We're making the commitment to use Smart Delivery on all our exclusive Xbox Game Studios titles, including Halo Infinite, ensuring you only have to purchase a title once in order to play the best available version for whichever Xbox console they choose to play on.
But during today's Xbox Games Showcase, first-party titles Forza Motorsport, Fable, Avowed, As Dusk Falls,Everwild and State of Decay 3 were all listed as coming to Xbox Series X and Windows PC specifically — with no Xbox One support and no Smart Delivery feature. Again, these are all games published by Microsoft's Xbox Game Studios, and almost all created by developers that Microsoft owns.