Joomla 6 for template users: what changed and what to check

Joomla 6.0 arrived in October 2025 as a major release, and Joomla 6.2 is now the current version. If you build or maintain Joomla sites, the important question is not “what is new?” but “what does this change about my template?”

The short answer: the visible design changes are modest, but the requirements and the upgrade path are not. Here is what actually matters when you are responsible for the template layer.

The PHP floor moved to 8.3

Joomla 5.4 runs on PHP 8.1 and later. Joomla 6 requires PHP 8.3 minimum, recommends PHP 8.4, and supports PHP 8.5 as of the 6.0.2 maintenance release. That single requirement decides whether an upgrade is even possible on your host.

Check three things before anything else:

• The PHP version your host actually runs, not the one in the control panel documentation.
• Whether your template and its extensions declare PHP 8.3 compatibility.
• Whether any custom code in template overrides uses functions removed or deprecated in PHP 8.3 and 8.4.

If the host is on PHP 8.1 or 8.2, the upgrade conversation starts with the hosting plan, not with Joomla.

Upgrading from 5.4 is an upgrade, not a migration

Joomla 6 is designed to be reached from Joomla 5.4. You do not rebuild the site or move content between installations. The official path is: update to the latest Joomla 5.4 release, then update to Joomla 6.

A detail worth knowing is the Behaviour - Backward Compatibility 6 plugin. It ships with Joomla 5.4 and does essentially nothing there — its job is to be present and enabled so that third-party extensions relying on it continue to work after the jump to Joomla 6. Leave it enabled during the upgrade.

That does not mean every extension is ready. It means the upgrade is less likely to fail halfway through because of a missing compatibility layer.

Your template overrides are the real risk

A Joomla template is not only CSS. Most serious templates ship overrides of core layouts under templates/<name>/html/. Every major release can change the markup those overrides replace, and Joomla 6 includes a substantial core refactor.

Before upgrading a production site:

1. List every override in the template, especially component views (articles, contacts, users) and module chrome.
2. Compare them against the Joomla 6 versions of the same layouts.
3. Test each overridden page on a staging copy, not on the live site.
4. Check whether the template author has released a Joomla 6-compatible update; if not, ask.

Overrides that only add wrapper classes usually survive. Overrides that copy large chunks of core markup are the ones that break.

Cassiopeia’s child template reduces the case for custom CSS

Joomla 6 ships a new Cassiopeia child template with extended colour and font options. The practical effect is that sites using the default template can change more of the design from the template settings, without maintaining a custom CSS file for every colour or size tweak.

Two implications for template users:

• If you maintain a Cassiopeia-based site, review whether custom CSS is still necessary; some of it can move into template settings.
• If you sell or maintain a separate template, verify that its settings still take precedence and that the child template does not introduce duplicate typography or colour rules.

The design intent is fewer overrides, not more. Treat any custom CSS you keep as something to justify.

Automatic core updates change your release discipline

Joomla 5.4 and 6.0 introduced automatic core updates. For template users this is a double-edged feature:

• Good: security patches arrive without someone remembering to click update.
• Risky: a core update can change markup that your template overrides depend on, and it can happen on a schedule you did not choose.

If you enable automatic updates on a site with a custom template, pair them with:

• Automated backups you have actually restored at least once.
• A staging site that receives the update first.
• A short post-update check of the pages with template overrides.
• A pinned template version you can roll back to.

Automatic updates are not a replacement for maintenance. They just move the maintenance to a different moment.

Small visible changes: transitions and motion

Both Cassiopeia and the Atum administrator template now use CSS transitions for page navigation. It is a small change, but it interacts with custom CSS:

• Template CSS that assumes instant state changes can look out of step.
• Animations you add yourself should respect prefers-reduced-motion.
• If the template ships its own transitions, check that they do not stack with the core ones.

This is cosmetic, but it is the kind of detail that makes an upgraded site feel unfinished if nobody checks it.

A pre-upgrade checklist for template owners

Before moving a site to Joomla 6:

1. Confirm PHP 8.3 or later on the target host.
2. Update to the latest Joomla 5.4 first, with the Backward Compatibility 6 plugin enabled.
3. Run the pre-update checker and resolve template and extension warnings.
4. Clone the site to staging and upgrade the clone.
5. Open every template override page and compare it with the original.
6. Test the mobile menu, forms, article layouts and module positions.
7. Check template settings for colours, fonts and layout options that may now overlap with core features.
8. Keep a rollback plan: files, database and the previous template version.

If you are choosing a template today, prefer designs that explicitly state Joomla 6 support and have a recent update history. Our template previews list the compatibility declared on each product page, and recent Joomla 6 designs such as JL Atlantic and Fintexy are built for the current release.

Joomla 6 is not a redesign of your site. It is a stricter baseline: newer PHP, a refactored core and a smoother upgrade path — provided you test the parts of the template that depend on core markup.

For the official details, see the Joomla 5.4 to 6.0 upgrade notes.