In early November, we announced the auto-migration to the new Google Sheets. We expect to see this migration in the U-M domain in the next two weeks. Though the migration will take several months to complete, users can begin taking advantage of the new features in Sheets as soon as their older spreadsheets are migrated. Simple spreadsheets will be migrated first, while spreadsheets utilizing Apps Script and other complex features will be migrated at a slower pace to ensure a more seamless transition. NOTE: You can tell what version your spreadsheet is by checking to see if there is a green checkmark at the bottom right of your spreadsheet. The checkmark is only found on new Sheets.
For more information, see An update on the migration of older spreadsheets to the new Google Sheets and Upgrading older spreadsheets to new Google Sheets.