Mark Whitten has revealed that Xbox 360 and Xbox One games will have different sets of achievements, and that players can boost their Gamerscore should they wish to play the same games on different platforms.
Speaking to IGN, Xbox One's chief platform architect explained how cross-gen achievements would work:
Every game has its own set of achievements, so if you're playing Call of Duty: Ghosts on Xbox 360 and on Xbox One, you can earn a separate set of Gamerscore in each game. But on the Xbox One version, you're getting a much richer set of features, such as seeing your achievements progress on the Xbox One console, being able to unlock new achievements throughout the year, and earning real prizes inside and outside of the game. Xbox One also enables a new concept of challenges, where games will be offering special time-based opportunities to earn various goals and collect the rewards.