Pantheon has updated the default PHP version for the Drupal 7 upstream to PHP 8.3, replacing the previous default of PHP 8.2.
New Drupal 7 sites created from Pantheon's upstream use PHP 8.3. Existing Drupal 7 sites that do not set php_version in their own pantheon.yml move to PHP 8.3 when they apply this upstream update.
Action required
Test the update before you deploy it to the Live environment. Apply it in Dev or a Multidev environment, confirm your modules and theme work on PHP 8.3, then promote it.
If your Drupal 7 site needs to stay on PHP 8.2, pin the version by setting php_version: 8.2 in your site's pantheon.yml before you apply the update. For steps, see Manage PHP Versions.
If you maintain a custom upstream, this change is not reflected in your pantheon.upstream.yml unless you update your fork from Pantheon's upstream.
