Thank you! You’re correct that ChatGPT is different from davinci. They’re both built on GPT3.5, but ChatGPT is trained on more conversational influences. However, davinci is really strong and will behave mostly like ChatGPT with the right conversation prompt :)
Yes, the GPT-3.5 model has been fine-tuned using RLHF, this is the text-davinci-003 you can use through OpenAI's API's.
Not sure if ChatGPT has some additional fine-tunings as you can get similar response using text-davinci-003, with the Chat prompt, and a temperature setting between 0.3 and 0.7.