As recently communicated, the auto-migration of older spreadsheets (those created prior to Dec 2013, including any subsequent copies) to the new version of Google Sheets will start today for Google Apps domains on the Rapid release track.
No action is required as a result of the migration. No data should be affected; however, in rare cases the results of some formulas and some other features may be slightly different. See "What's different in the new Sheets?" in the Help Center article for more detailed information.
You can tell what version your spreadsheet is in by checking to see if there is a green checkmark at the bottom right of your spreadsheet (the checkmark is found on new Sheets only).
Rapid release (gradual rollout); migration for Scheduled release domains will start in approximately four weeks (preceded by the notification)
For more information:Help Center
Note: all launches are applicable to all Google Apps editions unless otherwise noted
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