Earlier today, Apple released iOS 11.2 beta 2 to developers. The release notes accompanying the beta include the following announcement:
Soon, you’ll be able to offer new customers a discounted introductory price for your auto-renewable subscriptions on the App Store. iOS 11.2 introduces new classes … and new properties … to provide details on the introductory pricing and billing period you’ve selected for your auto-renewable subscriptions. You’ll be able to configure introductory pricing on your in-app purchase page in iTunes Connect soon.
Auto-renewing subscriptions were made available to all app developers with iOS 10 and already include the option to offer a free trial. With iOS 11.2 though, developers will have added flexibility to help them attract customers.