Out of curiosity, is $10/month prohibitively expensive for you or other developers? Copilot is free for open source developers and students.

It is not prohibitively expensive for me but it is a bit more than I would like to pay for such a tool. I hope that prices come down over time. Also, it is free for open source project developers and students but not for teachers and researchers, that is a little bit surprising to me.

Does Copilot use GPT-3 directly? I haven't found resources on this, but sounds doubtful?

It uses Codex, which is a descendant of GPT-3: https://openai.com/blog/openai-codex/