I guess the docs need to be updated?

Perhaps "You are guaranteed that the key is returned as a string" should be changed to "You are guaranteed that the key is returned as a symbol" for consistency? But I figured that's more of a breaking change.

Sounds like a breaking change to me :)

Is there any performance gain/regression happening with this change?

I wonder what our maintainers (@jkowens @namusyaka @olleolleolle and probably others) think of this change?

This issue has also been brought up in the Rails project. Since this models ActiveSupport::HashWithIndifferentAccess I would like to stay in line with the approach there. I'm wondering if we can also provide a method symbolize_keys that will serve as a work around.

See:

rails/rails#14643

https://bugs.ruby-lang.org/issues/9731

https://til.hashrocket.com/posts/d66e55091c-hashwithindifferentaccess-for-keyword-arguments