Weston Ruter

This is a temporary workaround for sites experiencing any issues with WordPress 6.9’s new ability to <a href="https://make.wordpress.org/core/2025/11/18/wordpress-6-9-frontend-performance-field-guide/#load-block-styles-on-demand-in-classic-themes" rel="nofollow ugc">load block styles on demand in classic themes</a>, for example <a href="https://core.trac.wordpress.org/ticket/64354" rel="nofollow ugc">#64354</a>.
If running a classic theme (i.e. not a block theme), it filters <code>should_load_separate_core_block_assets</code> to be <code>false</code>. This has the effect of reverting a change introduced in 6.9 where classic themes now load separate core block assets on demand by default.
Note that this plugin should be considered temporary until any issues are resolved in 6.9.1. At any time, you can test whether any issues remain by adding <code>?should_load_separate_core_block_assets=true</code> to any frontend URL; this restores the default behavior in WP 6.9.
This workaround is temporary because there are performance benefits to loading separate core block assets. They can be loaded on demand just when they are used, as opposed to loading the large single combined <code>wp-block-library</code> stylesheet. Loading separate block styles on demand reduces the amount of CSS which should improve page load time.

Load Combined Core Block Assets

Temporary workaround for sites experiencing issues with WordPress 6.9's new ability to load block styles on demand in classic themes.

Automattic

Donncha O Caoimh (a11n)

Jeremy Herve

Brandon Kraft

Devin Walker

Brad Jorsch

Eric Binnion

rheinardkorf

Nauris

Mark (a11n)

Andrei (a11n)

Pete (a11n)

Adnan Haque (a11n)

Ben Dwyer

Peter Petrov

danwalmsley

davidlonjon

Jaroslav "Dero" Polakovic

exelero

Karthik Bhat

Liam Sarsfield (a11n)

Speed up your WordPress site by optimizing page performance with Jetpack Boost. Easily activate one-click optimizations to boost your Core Web Vitals.
Did you know that a faster website:-
<ul>
<li>Ranks higher on Google.</li>
<li>Improves bounce rate (people stay on your site for longer).</li>
<li>Increases your conversion rate.</li>
</ul>
Increase your website performance and speed up your website with one-click optimizations that supercharge your WordPress site’s performance and improve core web vitals scores for better search engine listings.
Improving Core Web Vitals helps you rank higher on Google. A faster website also improves your SEO, helps you reduce your bounce rate and increase your ecommerce conversion rate.
<ul>
<li>Largest Contentful Paint (LCP): Measures loading performance. Improve your LCP and improve your website loading speed.</li>
<li>First Input Delay (FID): Measures interactivity. To improve user experience pages should have a low FID.</li>
<li>Cumulative Layout Shift (CLS): Measures visual stability. Lowering your CLS helps improve your user experience.</li>
</ul>
<h3>Performance Modules</h3>
Optimize your website with the same techniques used on the world’s most successful websites.
Each technique that is used to increase website performance is packaged up as a module that you can activate and try out.
Currently, the plugin has 6 performance modules available:
<ol>
<li>
Optimize CSS Loading generates Critical CSS for your homepage, posts and pages. This can allow your content to show up on the screen much faster, particularly for viewers using mobile devices.
Read more about critical CSS generation at <a href="https://jetpack.com/redirect/?source=jetpack-boost-critical-css" rel="nofollow ugc">web.dev</a>
</li>
<li>
Page Cache speeds up your site by saving pages as static files. These files are quickly served to visitors, reducing load times and enhancing user experience.
</li>
<li>
Defer Non-Essential JavaScript moves some tasks to after the page loads, so that important visual information can be seen sooner and your website loads quicker.
Read more about deferring JavaScript at <a href="https://jetpack.com/redirect/?source=jetpack-boost-defer-js" rel="nofollow ugc">web.dev</a>
</li>
<li>
Image Guide is a must-have feature for anyone who wants to optimize the images on their website. With this guide, you can ensure that the images on your site are the right size and dimensions, which is critical for improving user experience, page speed, and site ranking. Following the tips and best practices outlined in the guide, you can reduce image file sizes and speed up your site. Check out our <a href="https://jetpack.com/support/jetpack-boost/image-performance-guide/" rel="nofollow ugc">support page</a> to learn more about this feature and how it can help you achieve a faster and smoother website experience for your users.
</li>
<li>
Image CDN allows your site to serve automatically-resized images in modern web formats directly from Jetpack’s worldwide Content Delivery Network.
Read more about Image CDNs at <a href="https://web.dev/image-cdns/" rel="nofollow ugc">web.dev</a>
</li>
<li>
Concatenate and Minify CSS and JS combines and shrinks your JavaScript and CSS resources to reduce the number and size of requests to your server, ensuring your content loads faster.
Read more about minifying files at <a href="https://web.dev/minify-css/" rel="nofollow ugc">web.dev</a>
</li>
</ol>
Don’t want to have to manually generate your critical CSS each time you update your site? Let us do the heavy lifting for you with automated critical CSS – each time you update your site we will automatically regenerate your critical CSS and update your performance scores. Upgrading also gives you dedicated email support access.
<h3>With 💚 by Jetpack</h3>
This is just the start!
We are working hard to bring more features and improvements to Jetpack Boost. Let us know your thoughts and ideas!
We’d also like to give a special THANK YOU to the XWP team who provided help with initial research and scoping of the plugin and were engaged with our team throughout the project.

Jetpack Boost – Website Speed, Performance and Critical CSS

10 seconds, one click, and improved my site speed by 12%. I'll take it.

Quick and easy


Boost is an easy-to-use plugin. The interface to improve CSS is just one click! 


Very easy to use


Tackled request with care. Expert team has a superb experience.


Awesome app in the history

Speed up your WordPress site with one-click optimizations like Page Cache, Critical CSS, and Image CDN to improve Core Web Vitals.

Load Combined Core Block Assets vs Jetpack Boost – Website Speed, Performance and Critical CSS