OSPEAD (Optimal Ring Signature Research) is a recent study (April 2025) that measures anonymity efficiency and detected a risk: the attacker could guess the anonymous signature in 1 out of 4.2 cases instead of 1/16.

But beware: this is only a theoretical finding. So far, an "ospead fix" has not been implemented, because it would involve a hard fork, and the intention is to resolve it in a more comprehensive way with FCMP++.

So:

OSPEAD illustrates a real vulnerability in the selection of decoys, but there is still no technical solution in production.

The definitive solution will be part of FCMP++, which will robustly solve the modeling and privacy issues (and will arrive when the code is fully audited and tested).