The Vessel SDK provides access to the functionality of Vessel for developers to integrate the functionality of Vessel with mobile devices and to create applications for iOS devices. Vessel provides SDK access for both iOS (written in Objective-C) and Android (written in Java) devices. Vessel is a mobile application engagement platform that offers a variety of features for application owners to engage and keep users.
Google has apparently backtracked on the idea of allowing third-party messaging apps to access RCS on Android phones. Though RCS is a public specification, APIs are needed to connect messaging apps to the RCS protocols employed by wireless network operators. No API means no RCS for outside apps.