My prediction is that this becomes permanent. There is no good reason to be much more expensive than opus. At $4/$20 they are roughly at parity.

Making 2/10 permanent would be a killer move and make a strong argument against open-weight. For the sake of the open weight ecosystem I hope they do not.

Sol is much cheaper than opus because it uses less tokens. Never compare token pricing.

Isn't it essentially permanent since a new model will be out by then?

I'm guessing they do this to help move people off old models they want to depreciate. It's not a price hike for old models, it's them removing a discount!