Series X backwards compatible

It will probably become backward compatible with series x. In this moment the backward compatibility project for xbox one has been stopped, waiting for series x

And, if it were not backwards compatible, you might have to wait until the release of Xbox Series X, as they have said they have stopped working on bringing Backwards Compatible titles to Xbox One until the Series X launch to get Backwards Compatibility
up and running on the Series X. Form there, I imagine they will move back to bringing titles to both Series X and Xbox One for a few more years.

No further backward-compatible releases are planned as the team prepares for the launch of Xbox Series X. Reportedly, the Series X will be fully backward compatible with any release on the previous consoles, so there is a chance that it may well be playable.

Anything that currently works on Xbox one with very few exceptions will work on series X. If a game is not currently backwards compatible, the backwards compatibility program is currently suspended until after the series X launch with no guarantee to resume.

Yes. The game will be backwards compatible with the Series X.