Supersonic

Supersonic is the fastest speed class available in WipEout HD. It can only be attained by reaching zone 75 in a Zone Mode race.

On reaching Supersonic for the first time, the player will unlock the Trophy Zone Zeus.

This is widely regarded as the most difficult thing to accomplish in the game.

However, only a few tracks are designed to be able to handle SuperSonic:
 * Syncopia being reported to be able to go beyond Zone 100 glitchless.