Raptor is PayPal's JVM framework leveraged by over 1000 internal applications servicing over 100+ billion requests a day. These large-scale microservices, message daemons, and batch applications are the engine of the PayPal business. The framework team is ready to deliver the next major Raptor version with a primary focus of driving higher resource efficiency. This upcoming release, Raptor 4, aligns even closer to Spring, with Reactor enabling reactive programming to become mainstream at PayPal in 2020. This session will share the technical journey for moving PayPal engineers from a JAX-RS imperative programming model to a fully reactive stack. Thick with technical details, Raptor core engineers will be sharing the evaluation criteria, client and server benchmarking results, optimizations to RESTEasy, challenges, and next steps.