InstructGPT which is a "sibling" model to ChatGPT is 1.3B parameters. https://openai.com/blog/instruction-following/

Another thread on HN (https://news.ycombinator.com/item?id=34653075) discusses a model that is less than 1B parameters and outperforms GPT-3.5. https://arxiv.org/abs/2302.00923

These models will get smaller and more efficiently use the parameters available.