Same as Anthropic's similar offer, they're only giving 6 months free. This really just feels like a way to get OSS maintainers hooked so they buy subscriptions after the free period is over.
If they were really serious about supporting OSS, they'd offer it for free perpetually (well, with periodic checks to ensure the maintainers are still affiliated with the project). Anything less just makes it look like a marketing stunt.
And also, dumb how Github-centric this is, same as Anthropic's signup form. Most of my OSS contributions aren't on Github. Guess that means the projects I've worked on don't matter.