In a post on the official PlayStation Blog, social media manager Sid Shuman confirmed to a commenter that Metal Gear Solid: Ground Zeroes will be multiplatform.
Every main series entry (with the exception of Metal Gear Solid: Twin Snakes, a remake of Metal Gear Solid using the engine of MGS2: Sons of Liberty) has been exclusive to PlayStation platforms, up until now. Shuman didn't elaborate on which platforms exactly would be receiving Ground Zeroes, but the gameplay footage shown at PAX Prime 2012 was running on a high-end PC. One would expect Ground Zeroes to grace Xbox 360 as well.
Stay tuned to PSU.com for all things Metal Gear Solid: Ground Zeroes, including the world reveal gameplay footage.