ECU Mac Users Should Wait to Upgrade (posted Wednesday, September 30, 2015). OS X El Capitan, Apple’s latest operating system upgrade, is being officially launched today, September 30. However, ECU users should wait to upgrade to this newest version until all testing with ECU systems is complete. Remember, if there are incompatibilities between El Capitan and your installed applications or hardware, there is no downgrade option. The only solution is to re-image the machine and start over. Therefore, please wait to upgrade until testing is complete.