A projection of where the third wave of cognitive behavior therapy (CBT) may be headed is offered using acceptance and commitment therapy (ACT) as an example. The increasing emergence of a process-based therapy (PBT) movement is cited as having the potential to be transformative of psychotherapy more broadly, of third wave CBT approaches more specifically, and of ACT in particular, especially when combined with burgeoning efforts to develop a PBT approach informed by ongoing advancements in relational frame theory. If successful, it is suspected that the confluence of these influences may culminate in ACT and other third wave CBTs becoming less visible as their unique contributions are subsumed within what may be regarded as a gathering fourth wave of CBT, albeit one dominated by PBT. © Springer Nature Switzerland AG 2022.