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Pantheon Runtime Gen 2 upgrade on Aug. 18

If you have a website hosted on Pantheon, please read carefully — action is required before August 17. 

  • August 18, 2025: Pantheon will begin moving websites to PHP Runtime Generation 2.
  • We strongly recommend testing your website(s) before August 17.
  • The software for many websites is expected to change, which we anticipate will cause disruptions.
  • If your site runs on Drupal 7, uses Oracle with older versions of PHP, or relies on older versions of PHP extensions/packages, it is at a higher risk of breaking.

Starting August 18, 2025, Pantheon will begin upgrading all hosted sites to PHP Runtime Generation 2 (Gen 2). This is a significant infrastructure change that may cause disruptions to your site if not tested in advance.

We strongly recommend testing your site(s) before August 17 to ensure a smooth transition. If you are not ready, you must opt out of the automatic upgrade by August 17. Pantheon provides two options: opt in early and manage the upgrade on your own timeline, or opt out temporarily to delay it while you test.

What You Need to Do Before August 17

You must either:

If neither step is taken, Pantheon may automatically upgrade your Test and Live environments—and if your site breaks, rolling back will no longer be possible.

Sites Most at Risk - 
Please prioritize testing if your site:

How to Test Your Site

  1. In your Dev or MultiDev environment, add the following to your pantheon.yml file:
    php_runtime_generation: 2
  2. Commit and deploy. Test your site’s full functionality, including navigation, logins, forms, and integrations.
  3. If successful, promote to Test and then Live.
  4. To revert, change the setting back to:
    php_runtime_generation: 1

Why Is This Change Happening?

Pantheon is transitioning its PHP runtime to a new, Debian-based operating system with long-term support, replacing the CentOS-based runtime currently in use. This shift enables the use of system-managed PHP packages rather than compiled-from-source binaries, reducing container startup time and improving maintainability. It also streamlines the delivery of PHP updates and security patches, lowers platform-level technical debt, and positions your site to take advantage of newer PHP versions more efficiently and reliably. For details: Pantheon Gen 2 Overview

What's Changing?

You can find the full list of known changes and requirements on Pantheon's website.

Getting Help

If you run into issues while testing:

  1. Check Pantheon’s Known Issues
  2. Revert back to php_runtime_generation: 1 in your pantheon.yml to confirm the issue is Gen 2-related
  3. Submit a detailed support request via Pantheon’s Support Portal, and include “PHP Runtime Generation 2 Beta” in your message.

You can also contact us at webcontent@it.ucla.edu for guidance with testing or opting out.

Please take action by August 17 to avoid unexpected disruptions. We’re here to support you through this transition and ensure your site remains stable and secure.

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