NEW YORK, Nov. 5 -- People opening an X profile on a slow connection could spend less time staring at the platform's splash screen as the company rolls out a rebuilt website. But the improvement is not uniform: X's own measurements show a much bigger change for individual posts and profiles than for the Home feed.

Principal engineer Yagiz Nizipli says the new app already serves visitors who are not signed in, along with search-engine crawlers. Signed-in users are moving across one country at a time, with the older website remaining available while the migration continues. X has not provided a completion date in its engineering account.

The distinction matters because the biggest number is not a promise about every visit. X's headline de...