What changed
WordPress 7.1 “Mary Lou” was released on August 19, 2026. The post editor is now fully iframed for all themes, removing the older conditional behavior tied to block API versions and metaboxes. The final release also confirms that image compression, resizing and thumbnail generation now run in the browser through a WebAssembly build of libvips, alongside native AVIF, HEIC and HDR gain-map support and more resilient upload handling.
Why it matters
Plugins and blocks that reach into the editor DOM, inject styles into the wrong document, rely on legacy global selectors or assume a non-iframed canvas can break even when their PHP code is unchanged. The media changes also move meaningful processing work away from server-side PHP, which can reduce memory-limit and timeout failures but changes where extension authors should test hooks, upload flows and transformed assets.
The editor context is now consistently iframed
WordPress 7.1 makes the post editor fully iframed for all themes, matching the Site Editor. The editing canvas is separated from the WordPress admin interface, so admin styles no longer bleed into content and viewport-relative units and media queries target the canvas directly. That consistency simplifies the platform model but exposes extensions that depended on the prior non-iframed document structure.
Extenders should test DOM, assets and Block API assumptions
Plugins and blocks should verify where styles and scripts are enqueued, whether selectors cross iframe boundaries, and whether older block implementations rely on document-level assumptions that no longer hold. Browser automation and manual editor tests should cover editing, previews, inserters, sidebars, metaboxes and custom controls against the final 7.1 build.
Image processing now moves into the browser
The final release confirms that image compression, resizing and thumbnail generation run client-side via a WebAssembly build of libvips. WordPress says this reduces server load and avoids PHP memory limits or upload timeouts for large images. Native AVIF, HEIC and HDR gain-map handling, upload progress and automatic retries broaden the change beyond a simple editor UI refresh.
Other developer-facing additions broaden 7.1’s surface
WordPress 7.1 also makes the SVG Icon API public, extends the Abilities API with a filterable execution lifecycle and validation, adds theme.json support for responsive breakpoints and pseudo-state styling, and introduces design-system primitives for custom admin interfaces. These are separate from the iframe compatibility issue but make 7.1 a larger developer release than the pre-GA dossier could confirm.