The block editor for posts and pages does not make your theme a block theme. Theme architecture determines how you edit the surrounding site structure.
Identify your current theme
Open Appearance. If Editor opens the Site Editor with templates and global Styles, your active theme supports block-theme site editing. A classic theme commonly provides the Customizer and separate menus or widget areas. Plugins can alter the menu, so confirm the architecture in the theme's documentation or official listing if the interface is ambiguous.
For a developer checking files, a block theme has a block-based index template. A classic theme uses PHP templates. A theme.json file alone is not proof of a block theme: classic themes can use it too.
What changes in everyday use
| Task | Block theme | Classic theme |
|---|---|---|
| Change shared header or footer | Edit template parts in the Site Editor | Use theme controls, widgets, builder tools or code |
| Set site-wide design | Styles and theme-provided variations | Customizer or theme-specific controls |
| Change archive structure | Edit the relevant block template | Theme options or PHP templates |
| Create page content | Block editor, unless another editor is active | Block editor, unless another editor is active |
| Work with navigation | Navigation block | Theme menu locations and menu controls |
These describe the usual architecture. A builder or plugin can add another layer, and individual themes expose different controls.
Choose based on the changes you need
A block theme is a practical choice when you want to adjust headers, footers and templates visually with core blocks. You still need to understand that shared template parts affect multiple pages and that global Styles differ from local block settings.
A classic theme can remain a suitable choice when its layout and integrations already meet your needs. There is no requirement to rebuild a working site solely to use a different editor. Check update activity and compatibility before deciding to keep any theme.
For a new site, try your actual content with a maintained theme from an official source. A demo homepage does not reveal how long titles, complex menus or real product pages behave.
What switching does and does not move
Posts and pages remain in the WordPress database when you change themes. Their appearance can change because templates, colors, spacing and typography come from the new theme. Theme-specific shortcodes or builder elements can remain in content but lose their intended rendering if their supporting code is absent.
Menus, widget arrangements and editor customizations need review. Do not assume a block theme will reproduce your classic theme's header automatically, or that Site Editor changes transfer to every replacement theme.
Follow the safe switching process on staging. Compare your homepage, a post, archive, form and mobile navigation before making the change public.
Sources & verification
Sources checked September 23, 2026. Documented behavior is distinct from hands-on testing.