According to an Amazon France product page, Forza Motorsport 5 will have 24-player online multiplayer.
A translation of the description reads: "With 24 drivers for the first time on the same course online, do yourself a name among the gaming communities. The matchmaking system Smart Match offers a whole new multiplayer experience, fast and competitive, perfectly suited to your skills and style. Finally for the first time, Forza 5 benefit from dedicated servers."
If true, this sounds freaking awesome. Can you imagine 24 racers on a single course?
Elsewhere on the page, Amazon notes "more than 120 new [cars] available from the start," while also highlighting Kinect functionality and Drivatars, Forza's revolutionary AI that analyzes player behavior so it seems like you're playing with them even if you aren't.