That might still be true. But Microsoft has decided to retract part of its original promise to gamers.
Though originally, the company publicly and privately stated that all future in-house games (that is to say, those produced by Microsoft Studios) would be part of the Xbox Live Anywhere program, it turns out that some games may be exceptions to the rule:
"As head of Xbox, Phil Spencer has said that there may be certain unique games produced by Microsoft Studios in the future that aren't right for all devices and inputs," a company rep clarified by email.
In fact, Microsoft's promise that all future Microsoft Studios games would support Xbox Play Anywhere no longer officially exists. As reported by Gamasutra, the company quietly removed that wording from its official blog post last week. (You can find an archive of the original text here.)
Instead, Microsoft says that the only confirmed Xbox Play Anywhere titles are the ones specifically listed at its official website here.
However, Microsoft says it still intends to follow the spirit of its original promise. Here's the second part of the company's statement:
"Our intent, though, is to bring Microsoft Studios franchises and games to both Xbox One and Windows 10, and our goal to make as many Xbox titles as possible Xbox Play Anywhere has not changed."