I don't think this foundation would qualify.

I'm so incredibly not a lawyer, but my understanding is that educational 501c3s need to be predominately educational, in that they have classes and a physical location.

If the primary purpose of the Rust foundation is open source code and standardizing the language, it's not exactly educational.

For what it's worth, the Python foundation is a 501(c)3: https://www.python.org/psf/