One switch that runs A/B testing across every Send Email step in the sequence. You set Variants per step (2 to 5), what counts as a win, the confidence level to declare a winner, Max rounds per step, how many top templates to keep in rotation, how long to wait before counting a send, and the minimum lift worth promoting. The system picks winners, promotes each into the step's default template and drafts fresh challengers until the round limit is reached.