Base version gets PBT keycaps (yesss!) and Pro gets ABS (buuuh) Sadly not a typo. Hopefully the PBT set is available separately or (pretty please) PMK will make a custom run of the Ice-Cap.
https://kinesis-ergo.com/keyboards/advantage360/#faqs
"Which keycaps should I get? This one is easy…
Dye-Sublimation PBT: These are premium keycaps that are resistant to sheen and and fade. If you don’t plan to use the backlighting then this is the set you want. You have a choice of Dvorak or QWERTY legends. Shine-Through ABS: If you want to work in a low-light environment you’ll need to select these if you want to be able to read the key legends. This set is only available with QWERTY legends at this time."
They have a different sound & feel, and the colorways achievable are more vibrant.
There are reasons for ABS