YouTube's AJAX interface seems to be publicly available, at least for Chrome users. Back in May, I noticed a red progress bar at the top of YouTube's pages when loading a new video: YouTube experimented with the HTML5 history.pushState to change the browser URL without reloading the page. Then YouTube's engineers detailed their plan to make YouTube pages load faster. In the new interface, the video player and the JavaScript/CSS files are only loaded once, so when you click a new link, YouTube only loads the HTML page and the video. This happens almost instantly.
For some reason, the AJAX interface currently launched by YouTube only works when you click a related video or when you load a playlist. It doesn't work yet for the homepage and search results.
