To fully exploit the business opportunity available through application programming interfaces (APIs), your designers must consider each API's purpose and audience as they answer a wide range of technical design questions. API security is a foundation for robust API-based applications. Your versioning strategy must make it easy for your API users to track API changes. Open-ended design can allow your APIs to support a wide range of future scenarios. As part of a series on API design practices, this report examines five scenarios for API security and best practices for version management and open-ended API design.