As part of our ongoing platform maintenance and security improvements, Drush versions 5 and 7 are no longer available on Pantheon. Sites currently configured to use Drush 5 or 7 are being automatically upgraded to Drush 8 over the next few days.
Drush 5 reached end-of-life (EOL) in May 2015 and Drush 7 in July 2017. EOL software does not receive security or feature updates, and could expose sites to attack if any vulnerabilities or exploits are discovered.
Find out which version of Drush your site is running.
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While all sites previously using Drush 5 or 7 have been auto-upgraded to Drush 8, the pantheon.yml file for these sites have not been changed and will still contain the retired values. In the future, this will cause a git push to the platform to be rejected. Customers with sites configured for Drush 5 or 7 should upgrade the Drush version in pantheon.yml to at least Drush 8.
Sites created with custom upstreams using EOL Drush versions may also have unexpected behavior upon site creation. Upstream updates may also fail if pantheon.yml is updated while drush_version is still set to 5 or 7.