Hey, man, sorry for the late response. I'm a bit lazy about checking the forums.
I believe what you're referring to is the references in the Companion about trading off spell casting levels to pick up generic class abilities. By deciding not to advance a level as a spellcaster, the Arcanist can instead gain a Generic Class Ability at that level, with the GM's approval.
That means that, for example, you could choose when you reach 3rd level to pick up a Generic Class Ability instead of gaining a level of spellcasting. In this case your spellcasting would remain at level 2, but you'd get the Generic Ability you chose. Generic Class Abilities are found in Book Two of the AA Core Rulebook. The Companion posits that in such a way you could, feasibly, use the Arcanist as a sort of "Generic" class, by never advancing in spellcasting, but picking up Generic Class abilities instead.
Now, personally, as a GM I don't know that I'd allow that in such a pure form. It would result in a very powerful character who gains a new ability every single level.
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