https://www.gamespot.com/articles/gta-5-onlines-transform-races-mode-releases-next-w/1100-6454060/

A new mode is coming soon to Grand Theft Auto V. Beginning October 17, GTA Online players will be able to take part in the much-anticipated Transform Races, a new type of race that Rockstar describes as the "next evolution of Stunt Racing."

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.