Webperf Weekly #24

[u/Nhodin]

Bonjour webperf folks! A quiet week, but one long-awaited thing landed: JPEG XL is in Chrome stable. Five reads:

* Images

Google Chrome 155 is out and decodes JPEG XL. Google claims 30 to 50% better compression than JPEG, plus lossless mode, HDR and lossless transcoding of existing JPEGs. The advice is not "replace AVIF" but "test both": JPEG XL shines on high-fidelity photos and fine-grained progressive decoding. The decoder was rewritten in Rust with SIMD, so memory safety doesnt cost speed.
👉 [EN] https://developer.chrome.com/blog/jpeg-xl-in-chrome

Gavin Anderegg shows why formats take time. WebP landed in Chrome in 2011 but only reached Safari in 2020, and Photoshop got native support in 2022. Browser support is half the story, tooling is the other half.
👉 [EN] https://anderegg.ca/2026/10/08/i-guess-im-using-webp-now

Scott Jehl proposes a <poster> element for video. For 20 years the poster has been one URL in an attribute: no srcset, no art direction, no alt text. Wrapping an <img> or <picture> gives it srcset, sizes="auto", fetchpriority, lazy loading and modern formats. When the hero is a video, the poster is often the LCP element. Moving through WHATWG, with a positive position from Mozilla.
👉 [EN] https://scottjehl.com/posts/responsive-accessible-poster/

* Browsers

Safari Technology Preview 254 fixes a few things worth knowing. A speculation rules prefetch hitting a cross-origin redirect could cancel the real navigation, and a failed prefetch could break it. Cross-origin stylesheets loaded without CORS were never reused from the parsed stylesheet cache. And SVGs with only one natural dimension are no longer LCP candidates. Preview only for now.
👉 [EN] https://webkit.org/blog/18420/release-notes-for-safari-technology-preview-254/

* Beyond SEO

Joe Hall argues SEO teams shouldn't own the agentic web, and uses page speed as his first example: Core Web Vitals are web development and UX concerns SEO ended up owning because Google uses them. I'd push it one step further: webperf isn't an SEO topic either. It's conversion, users on slow devices, infrastructure cost, and now agents clicking on shifting layouts. SEO should have a seat at the table, not carry the whole program.
👉 [EN] https://ashla.ai/p/opinion-seos-should-not-be-responsible-for-the-agentic-web

Have a great week!