The first mode expected to be available later this month is Transform Races, which is dubbed as "the next evolution of stunt racing in Grand Theft Auto Online".
Unlike in a typical Stunt Race, during a Transform Race, your vehicle will be changing between bikes, planes, and more depending on the terrain. As you can see in the trailer above, these transformations happen instantly when you hit a specific point on the course, which should keep races constantly surprising. This will allow players to instantly switch vehicles and race types - from land one second to the air or the sea the next - thanks to the flawless transition of unique stunt tracks. Manhunt-like Condemned and Dogfight aerial battle game modes will be included in the update as well.
The video released by Rockstar provides a self-explanatory look at what to expect.