ACT is entering its 40th year of development. Despite its undeniable historical origins in behavior analysis, extensive basis in behavior analytic research, and now enormous body of empirical research supporting its basic claims, some are still arguing that ACT is not legitimately part of behavior analysis. We agree with the target article that it is. We argue, however, that critics are right to feel that ACT will disrupt the field. It will do so not because of ACT per se, but because it brings relational frame theory (RFT) in with it and vice versa, and relational operants operate on other behavioral processes. This empirically established effect means that the vast literature on direct contingency control will need to be reexamined piece by piece while considering relational learning abilities. Such an agenda is exciting, but it is also daunting and disorienting. For behavior analysis to reject either ACT or RFT, both must be rejected. That appears to be the only way to avoid the coming disruption, but the cost would be in the distortion of the field itself that would result. Sometime the products of a scientific field require a fundamental rethinking of that field. In our view, that is the situation behavior analysis now faces. It is a kind of test, and we do not yet know if behavior analysis will pass it.