They switched from ring to aws-lc-rs as the default crypto-provider in release 0.23.0 / 29th of February 2024. Both the above as well as the earlier blog post from last year (see the thank you section at the bottom) already takes this change into account.

On the other hand that suggests to me that a C-project like curl would not benefit from this library in terms of performance and could just use aws-lc directly. And I doubt curl has any intentions of switching to Rust as the main language.

Rustls to me seems useful for Rust projects that want to implement HTTPS clients or servers. I do use it in one of mine, but kept using ring as the crypto-provider as it is a little easier to build and the performance for my projects use cases is sufficient.

Right, so in that case, when users build curl against the rustls library instead of aws-lc or openssl, they will under the cover use aws-lc-rs, which is a rust wrapper on top of aws-lc.

So what I then would be interested, too, would be to see a comparison of the performance of different uses of curl built with different TLS-backends. I would naively expect it to perform better when using aws-lc natively, instead of using the rustls -> aws-lc-rs -> aws-lc indirection. I might be wrong - and there may be other benefits to using rustls with curl.