Pantheon has updated the default PHP version for the WordPress and WordPress (composer managed) upstreams to PHP 8.3, replacing the previous default of PHP 8.2.
New sites created from these upstreams use PHP 8.3. Existing 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 plugins and theme work on PHP 8.3, then promote it.
If your 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.
