Cohen–Lenstra–Martinet–Malle conjecture for even-degree class groups

Let $K$ be a nowhere-evenly-ramified number field of even degree $n$ with real signature $(r_1,r_2)$. Enumerate such fields by discriminant. Cohen–Lenstra–Martinet–Malle conjecture. The average value of the size of the $2$-torsion subgroup of the class group is

$$\#\operatorname{Cl}(K)[2]=1+2\cdot 2^{1-r_1-r_2}.$$

This prediction concerns the exceptional even-degree setting of nowhere-evenly-ramified fields and is part of the Cohen–Lenstra–Martinet–Malle heuristic framework. The supplied text does not provide evidence that the prediction has been proved or disproved.