You go through PSC as if you are the needed level.

So you're calibrated as if you are a 5. But if you're still a 4 because you're not delivering as a 5... then you'll fail to meet expectations, naturally. The rest sort of takes care of itself.

Pro tip: ask them for the severance instead of the PIP, and GTFO.

One or the other, I think they usually try to put you on a PIP before firing though. It can feel like an up or out kind of culture, but the timelines are fairly reasonable IMO - e.g. they give you 5 years to progress from an entry-level SWE to mid/senior-level SWE (L3 -> L5).