Twilio has announced the open-sourcing of its OpenAPI specification for all Twilio APIs, making it easy for developers to access and generate code for their preferred programming languages. This allows users to build with Twilio using popular tools and environments without writing complex methods and functions. The new feature also enables client library generation, mock testing, and support for Postman, a free development tool for making API calls. With the OpenAPI specification, developers can now auto-generate code, programmatically build libraries, and test their applications with Twilio's APIs more efficiently.