Here are my reasons why this "upgrade" is, in experience, a huge downgrade for Plus users:
* The quality of responses from GPT-5 compared to O3 is lacking. It does very few rounds of thinking and doesn't use web search as O3 used to. I've tried selecting "thinking", instructing explicitly, nothing helps. For now, I have to use Gemini to get similar quality of outputs.
* Somehow, custom GPTs [1] are now broken as well. My custom grammar-checking GPT is ignoring all instructions, regardless of the selected model.
* Deep research (I'm well within the limit still) is broken. Selecting it as an option doesn't help, the model just keeps responding as usual, even if it's explicitly instructed to use deep research.
Projects seem broken as well. Does not follow instructions, talks in Spanish, completely ignores my questions, and sometimes appears to be having a conversation with itself while ignoring everything I say. I even typed random key presses and it just kept on giving me the same unwanted answer, sometimes in Spanish.
* The quality of responses from GPT-5 compared to O3 is lacking. It does very few rounds of thinking and doesn't use web search as O3 used to. I've tried selecting "thinking", instructing explicitly, nothing helps. For now, I have to use Gemini to get similar quality of outputs.
* Somehow, custom GPTs [1] are now broken as well. My custom grammar-checking GPT is ignoring all instructions, regardless of the selected model.
* Deep research (I'm well within the limit still) is broken. Selecting it as an option doesn't help, the model just keeps responding as usual, even if it's explicitly instructed to use deep research.
[1]: https://openai.com/index/introducing-gpts/