In modern accelerators particles collide with their anti-particles and can annihilate, so the available energy includes both the kinetic energy and the rest energy of the colliding particles in the center-of-momentum frame before the collision.
Modern particle accelerators involve collisions between particles and their corresponding antiparticles, resulting in potential annihilation. The total available energy includes both the kinetic energy and the rest energy of the particles involved in the collision before it occurs.