Isn't it that models themselves are public (like BSIM) but what you get in a PDK is a macromodel wrapping BSIM with another zillion of fudge factors, or at least binned by device size? That's what I understood by peeking into various PDK models.
Not every fab use BSIM models. Philips (now NXP) use PSP models for their own fabs and implement them as verilog-a code. This is a physics based model instead of fitted model like BSIM.
TSMC has their own C-library on top of BSIM models for FinFETs because BSIM isn't covering what they need. I don't know what will they use for GAA stuff.
