Comment by MacsHeadroom

The speed-up of the free and default "chatGPT" happened because they switched it from the full size GPT-3.5 to "GPT-3.5-Turbo", which is likely a finetune of the 10x smaller GPT-3 Curie.

If you have chatGPT Plus you can choose "Legacy" from the drop-down to get the smarter (and slower) 175B Parameter version of GPT-3.5. That version is the same speed as GPT-4 when load is low (early morning EST), which lends credence to the theory that GPT-4 is the same size as overparametrized GPT-3.