Up to this point, actual gameplay of Final Fantasy XIII has never been shown. There have been many screenshots and trailers of the game, but none of these have included a hint as to how the battles will work. This should change before the end of 2008.
The latest issue of Gemaga magazine has an interview with Tetsuya Nomura, director of Final Fantasy XIII (amongst other duties at Square Enix), where he states that battle gameplay from Final Fantasy XIII will be shown before the end of this year. In Japan, Final Fantasy XIII will be released exclusively for the PlayStation 3, but the North American version will be released on both the PlayStation 3 and Xbox 360.
Nomura also explained that the current screenshots of Final Fantasy Agito XIII, which show three characters being controlled in battle, are of a temporary battle system. The final battle system will involve more than just three characters in the player's party. Final Fantasy Agito XIII will be released only for the Sony PSP.
A demo for Final Fantasy XIII is planned to be included with the upcoming Blu-ray version of Final Fantasy VII: Advent Children, called Advent Children Complete, along with high definition trailers for Final Fantasy XIII and Final Fantasy Agito XIII. Advent Children Complete has a Japanese release date of March 2009. Final Fantasy XIII and Final Fantasy Agito XIII do not have Japanese or North American release dates yet.