What's the difference between APIs and MCPs?

APIs are the legacy approach for connecting to a service, useful when you want to build a custom application. One example: a 3,000-person firm used a company's API to build their own internal chatbot on top of a database, since APIs are highly customizable and let you build applications on top of them, but require more work and you manage an API key yourself. MCPs (Model Context Protocol) connect directly into your applications through a 'harness'—a workflow layer that sits on top and lets an agent do the work for you. MCPs require less setup than APIs and are meant to connect tools directly into an AI assistant like Claude.