alt Hacker NewsGithub gives Copilot Pro to open source maintainers but they don't really tell you what the requirements are. I have it and I just get a notification every month that it's been renewed and I never even applied for it. I assume it's a combination of activity on github and popularity of your repositories.
I work for a commercial open source company, working on the open source product. I applied for it way back in the day and got it, and i still get the emails every month saying that they renewed my free grant.
This is all despite the company also paying for Github Copilot.