The REST API documentation published here on the Magento 2 Developer Documentation website describes the REST APIs that are available on the latest release of Magento 2.
This documentation uses ReDoc to organize and present schema files that follow an Open-API specifications. The schema files this tool uses are generated from a running instance of Magento 2.3, and it represents the state of the code at the time the file was generated.
You can also create a dynamic REST API documentation set on your server with live data. Magento uses Swagger to display REST APIs for all installed products and allows you to try out the APIs. For more information, see Generate local REST API reference.