Endless Boost is the fourth Challenge Act of Rooftop Run Act 2 in the console/PC version of Sonic Generations. It is unlocked after clearing every Stage in the modern era and is playable only as Modern Sonic.
This Act takes place within a slightly modified section of Rooftop Run Act 2. The final section where the player must knock Egg Fighters into Aero-Chasers has been made more difficult, with swinging axes, lightning traps, and bombs placed in the player's way. The player also cannot collect any Rings (despite the fact that there are some placed in the Act), and must avoid taking damage in order to survive.
The player begins by running into the aqueduct near the end of the stage. They must navigate past enemies, swinging axe blades, and other obstacles while running to the Goal Ring at the end of the course. The Act otherwise progresses identically to the normal version, and the player must dodge some spiked barrels dropped from the Eggman Flying Battery just before reaching the Goal Ring.