Block Theme vs Classic Theme

A block theme is a WordPress theme architecture that uses HTML templates assembled from Gutenberg blocks (including site-wide elements like the header and footer), while a classic theme uses PHP template files and only renders blocks inside the post content area — the central architectural choice for any new WordPress build today.

What block themes change

• Site editor: editors can modify the header, footer, archive layouts, and 404 page through the block UI rather than asking engineering for template changes.
• theme.json: a single JSON file controls site-wide design tokens (colors, fonts, spacing), enforced consistently across blocks.
• Templates are HTML files containing block markup, not PHP.
• Patterns become the unit of editorial reuse, registered in PHP but composed in the editor.

When classic themes still make sense

• Heavily customized PHP templates with complex query logic that doesn’t translate to the block editor.
• Sites running plugins or page builders that don’t support block themes.
• Legacy editorial workflows where contributors expect the classic editor experience.
• Specific theme functions (custom hooks, deep parent theme customizations) that the block-theme architecture doesn’t yet expose.

What Hello World ships

New builds default to block themes with custom block patterns matching the design system. Editorial autonomy is a goal: comms staff should be able to build new pages from existing patterns without engineering involvement. For migrations from older WordPress sites, we evaluate per-engagement whether to ship a block theme or a classic theme with block editor support — that decision lives in Define.