This is very interesting because the free version is 3.5 but you can use a GPT (official from Open AI) called "ChatGPT Classic" which uses version 4. Loophole found!
"Custom GPTs open for free ChatGPT users" from The Verge
"OpenAI rolled out new features to free ChatGPT users, including custom GPTs, data analytics, and vision — capabilities previously locked to paying subscribers"
https://www.theverge.com/2024/5/29/24167436/chatgpt-4o-custom-gpts-free