It really depends on so many factors it’s extremely hard to tell. We’ve brought folks at Cloudflare up to speed roughly that fast.

“average” and “proficient” are both very variable in that statement, imho.

Depends on your definition of average: I found that to be the case with significant programming experience with traditional languages (notably not something like Haskell) so I think it’s plausible since the compiler, editor, and documentation are rather above average for newcomers. In particular, Cargo providing a lot of easy tools and the compiler providing really helpful error messages seemed to be useful for the time to write a real first program which does something useful.

Edit: one other big factor - presumably in their environment you have coworkers to get advice from. That’s huge when you’re first starting.

We became pretty comfy with it in less than a month in Aug 2017. (Let's say average guy had a few years of Python and this-and-that before that, and a ~5 year CS degree before that.) Sure, there was no async/await anywhere yet, but no crossbeam-channels either. And there were a lot less friendly tutorials and there were a bit more rough edges. (Especially that we did "IoT" so cross-compiling was ... an experience.)

IME it takes 2-3 months for a talented senior developer to get comfortable with it.

”Several weeks of hard effort”, they said. I can buy it, if they actually work hard and are basically competent. Rust is a difficult language in total, that’s for sure, but you can get a lot done without knowing it all.