http://www.polygon.com/e3/2016/6/13/11923410/we-happy-few-coming-to-xbox-one-preview-next-month

I thought Xbox Preview was for Xbox features, not games. Does this mean it's free or what?

They introduced last year at E3 that games would be available in early access, just so far all the games that have been in it have been pretty lackluster. I don't believe it'll be free, I think you get it for a discount if you buy it in early access.

Here's an article about it: http://arstechnica.com/gaming/2015/06/xbox-game-preview-brings-early-access-to-xbox-one-adds-free-demo-options/

They do have free demos for a lot (if not all) of them.

Thanks, Xenos. I probably saw some of these and did not realize that they were exclusive previews.

The key phrase there being "Game Preview" rather than "XBox Preview."

Game Preview is a similar sort of program to Steam Early Access, where games are available to buy before they're deemed complete. Players can buy and play the game in this unfinished state, and (potentially) offer feedback. The Game Preview games are pretty heavily discounted compared to the final retail price.