Legacy Dashboards vs New Dashboards (Beta) in the UI
Currently, new reports are available in sandboxes only, where you can view the new report module AND leave the legacy reports active. When both report "modules" are active in your environment, you will see two report navigation icons in the toolbar. Hover your cursor over each icon - you will see one labeled "Reports" (the legacy reports), and one labeled "Reports (Beta)" (the new reports). See the screenshot below:
The "reports" icon will take you to the legacy reports UI; the "Reports (Beta)" icon will take you to the new reports UI.
When the new reports are available for use in production (while still Beta), we will leave the legacy reports active as well, unless you specifically ask us to disable them. If you have a sandbox, both the legacy and the new reports will be enabled by default.
At some point in the future (with plenty of notice), the legacy reports will be deprecated.