Signed Exchanges (SXG) allow trusted third parties, like Google Search, to cache and serve web pages with the site’s domain. The purpose of SXG is to dramatically improve site performance and deliver near-instant page delivery to visitors without requiring AMP.
The AMP alternative is more appealing and convenient for sites to use, but its adoption has been slowed by its complexity and being limited to mobile search results. Cloudflare solved the complexity problem by automating SXG for Google Search, and now Google has announced it will be supporting SXG for its desktop search results.
Devin Mullins, a software engineer at Google, made the announcement on Google Groups and tweeted about it. In addition to supporting SXG on desktop search results, Mullins provided details on how sites could opt out of Google using SXG on desktop or mobiles results.
Google Search is planning to launch SXG support for desktop users in the coming weeks.
Sites using responsive web design or separate mobile/desktop URLs don’t need to take action.
Sites using dynamic serving (varying by User-Agent header) will need to annotate their pages as mobile- or desktop-only, as documented here. For example:
<meta name=supported-media content=”only screen and (max-width: 640px)”>
Otherwise, desktop users may see the mobile version of the page.
We’re reaching out individually to SXG sites who we’ve found to use dynamic serving, but I wanted a broad announcement in case there are any that we miss.
If you have any questions, please ask on the Google Search Central Help Community or the webpackager Q&A board.Devin Mullins via Webpackaging Announcements on Google Groups
supported-media meta tag is a draft proposal, but Google Search will still be implementing it soon regardless. Google stated that conventional methods for serving different HTML have “conflicts with caching by upstream intermediaries,” and this meta tag is the best method to use for SXG.
No timeframe was provided for when SXG support in desktop results will go live other than soon. Additionally, SXG only works in Chrome, Chrome variants like Edge, and Opera. Safari and Firefox still do not support SXG.