Source?

There are at least three proposals in flight for C++26, if they reach an common agreement on time, or it has to be done by C++29, remains to be seen.

Just search for the various revisions,

https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/

I'm not even using Rust but I think you should stop hyping things that won't exist for years as if they were real and proven, like you've been doing a lot.

I've had a quick look at one of the proposals behind the link and it's no comparison with the existing Rust way. Even std::variant itself is a crutch (being templatized by a list of types), not comparible with true algebraic datatypes.