It seems that Apple really wants its customers to buy its new iPhones because according to a report from MacRumors, it looks like Apple is offering up customers more credit when they trade in an older iPhone and are looking to get either the iPhone XR or the iPhone Xs. Note that this is a limited time offer so you might want to move fast.
Apple boosting some iPhone trade-ins by $100 toward iPhone XR and XS
If you're holding onto an iPhone 5s, you're not getting any extra credit and neither are iPhone X owners. But you've lucked out if you've got an iPhone 6s.