WordPress 6.4 will be shipping a new default theme, Twenty Twenty-Four (TT4), expected in early November. This theme is more feature-rich than previous default themes, and contributors have been working on identifying potential performance improvements that can be made ahead of the release.

As a starting point, Google-sponsored Performance team contributor Felix Arntz conducted several benchmarks comparing TT4 with the TT3 block theme. These included overall Web Vitals covering both server-side (TTFB) and client-side (LCP-TTFB), along with a separate server-side load time performance benchmark. Arntz posted a summary of this data:

• For the home page:
  • Overall load time (LCP) is 58.8% slower.
  • Client-side performance (LCP-TTFB) is 93.5% slower.
  • Server-Timing (wp-total) is 71.8% slower.
• For the singular post:
  • Overall load time (LCP) is 3.9% slower.
  • Client-side performance (LCP-TTFB) is 40.1% faster.
  • Server-Timing (wp-total) is 42.3% slower.

He noted that the reason TT4 is slower is because it provides a lot more feature rich content out of the box than TT3.

“Interestingly, the server-side performance difference between TT4 and TT3 seems to come almost exclusively from the number of block editor features used by the theme, but not by any problems from the theme itself,” Arntz said. “In fact, the theme only includes a single function of PHP logic. It does however include more complex content than TT3 and comes with a large number of patterns, so potentially that plays a role there.”

After just two weeks of work on specific tickets for a few flagged issues, performance contributors were able to make the new Twenty Twenty-Four theme (and other themes) load more than 40% faster.

“I am very excited to report that most (if not all) of the server-side performance concerns have been addressed, via additional general performance fixes that landed in core,” Arntz said.

He summarized the improvements in the server-timing benchmarks when comparing TT4 and TT3 with the latest core trunk:

• TT4 home page loads in 85.91ms, compared to 78.08ms in TT3.
  • → 10.0% slower, but before was 71.8% slower 
• TT4 “Hello world!” post loads in 96.44ms, compared to 86.35ms in TT3.
  • → 11.7% slower, but before was 42.3% slower 

There are a few outstanding client-side performance enhancements, but Arntz said these require more thought and time investment so they have been milestoned for the 6.5 release. 

WordPress 6.4 Beta 3 was released yesterday. Although the flagship Font Library feature has been punted to 6.5, contributors said this change will not affect Twenty Twenty-Four, as the theme will ship with preselected fonts that get loaded from the theme assets, just like previous default themes.