As part of our continued effort to protect and secure customer sites, the Pantheon platform will no longer offer PHP versions 5.3 and 5.5 as of February 25, 2025.
PHP 5.5 was declared end-of-life (EOL) by the PHP Foundation on July 21, 2016, more than eight years ago. EOL software does not receive security or feature updates, and could expose sites to attack if any vulnerabilities or exploits are discovered.
We will soon provide long term support (LTS) security coverage for the remaining EOL versions of PHP on the platform.
Action required
Customers with sites using PHP 5.3 and 5.5 should test and upgrade the PHP version to at least PHP 7.2. If no action is taken, sites using PHP 5.3 and 5.5 will be auto-upgraded to PHP 5.6 on February 25, 2025. Pantheon currently recommends at least PHP 8.1 for all production sites.
Sites created with custom upstreams using EOL PHP versions may also have unexpected behavior upon site creation.