6 months is what I heard. I'm currently at ~2 and 6 sounds like a pretty good estimate.

It takes a relatively short time to be proficient enough to make useful contributions, maybe half a year to a year to be confident. You can give an experienced developer the Rust book and have them contributing to a Rust codebase quickly.

For me it was ~2 weeks to get out of "learning mode" and into actually writing production code. 3 months to feel proficient. Maybe a year to feel that I had reached parity of fluency with languages I already knew.

People really vary, it felt natural to me almost immediately but Rust's surveys indicate that some noticeable proportion of respondents report not being comfortable after more than a year.

This is seen as an important thing to improve because of the slogan "A language empowering everyone to build reliable and efficient software". If Rust isn't empowering everyone because say, 10% of people who try to pick it up can't get anywhere that's not good enough.