What file format is used to save Power BI Desktop reports?

Power BI Desktop reports are saved in the .pbix file format. This format is specifically designed for Power BI and allows users to store and manage not only the data models and visualizations created within the application but also the queries and the connections to the data sources. The .pbix format is optimized for the features and capabilities of Power BI, facilitating easy sharing, collaboration, and publishing of reports to the Power BI service.

In contrast, the other file formats are not suitable for saving Power BI reports. The .xls format is used for Excel spreadsheets, the .ppt format is for PowerPoint presentations, and the .csv format is for comma-separated values, which primarily involves data storage without any visualizations or report elements. Therefore, the .pbix file format is uniquely suited for Power BI's comprehensive reporting features, making it the correct choice for saving Power BI Desktop reports.