As we saw in the previous section, Reactor is rich in useful operators. Furthermore, we may have noticed that the overall API has similar operators as in RxJava. However, what is the main difference between the old generation of libraries and the new one, which includes Project Reactor 3? What is the most critical breakthrough here? One of the most notable improvements is the Reactive Stream life-cycle and operator fusion. In the previous section, we have covered the Reactive Streams life cycle; now, let's look at Reactor's operator fusion.