As modern applications become increasingly feature-rich and performant, user expectations are at an all-time high, making it essential to communicate key information promptly and accurately. To achieve this, developers can utilize specialized communications APIs that provide features like real-time order update emails, push notifications, and live chat with sales and support. Communications APIs have evolved into three core types: App-to-user APIs, which form a core part of the application experience, sending transactional messages instantly; Brand-to-user APIs, used for sending targeted messages to specific groups of users, saving engineering time but often with implementation delays; and User-to-user APIs, facilitating active conversations between individuals, whether internal staff or app users. By understanding the strengths and weaknesses of each type, developers can create a seamless user experience while enabling their teams to save time and work efficiently.