alt Hacker NewsDepends if they are using another CI provider or running Jenkins themselves.
But also, Circle CI would be a known cost change. Right now, the only thing you know is that GitHub wants to start charging money. You have no idea what new pricing model they come up with.
Self-hosting all of your CI is yet another tradeoff. The software comes for free (if you're using Free Software, that is), but you now have operational overhead. I'm not saying it's an unreasonable move, but it's also not a free swap