Prestige Classes are available as normal provided you meet their prerequisites.
The following changes are in effect for translating prestige classes for Spheres of Power:
Spell Prerequisites are exchanged for their equivalent talents.
Arcane, Divine, or Psychic spell casting prerequisites apply based on your selected casting tradition. If you have a custom tradition you are counted as the category of whichever tradition is closest to yours.
Wherever a Prestige Class gives Spellcasting Level +1 you gain talents as one of your non-prestige classes, and your Caster Level increases as if you had gained another level in the same class. For example a Mid-Caster would still need to have two levels in a prestige class where both levels give Spellcasting Level +1 to have their CL increase.
Any ability that grants a new known spell instead grants an equivalent talent. If the ability would grant multiple known spells it grants half as many talents.