constexpr on a variable declaration does that (i.e. it's still superfluous on function declarations, which is where it clutters code by far the most). But even for that, there was already std::integral_constant which would've forced this, and they could've just updated it to C++20 via template<auto Value> static const auto constant = Value; if they really wanted to. Or added an [[attribute]] for variable declarations, just like how we have [[likely]] etc. No need to introduce a whole new keyword for this, especially not in a ton of other contexts.