What's the criteria for being considered "a maintainer of a popular open source project"? They never actually publish the criteria anywhere from what I can tell. They just say visit the subscription page and if you are eligible it should be available to you and if you see a charge then you are not eligible. I think though they should still be transparent about what their metric is for determining popular projects on GitHub; otherwise, the code that determines eligibility might be broken and no one would be able to tell. Or worse they could just be lying about it entirely.

At a minimum, 4.3k stars is not enough, because I don't qualify.

This is curious - I maintain 2 projects with 2k cumulative stars, and I was able to claim the free access. Wonder what the metric is? Maybe creation date has something to do with it?

If you want to check if you qualify: https://github.com/github-copilot/free_signup