PageSpeed Insights: Lighthouse 13.6 May Raise Scores

PageSpeed Insights now tests pages with Lighthouse 13.6.0, released on October 27, 2026. The update changes how page load is simulated, and according to Barry Pollard of Google's Chrome team, performance scores will generally go up without any change to the site. It matters to anyone comparing speed reports over time.

What we know

The release: Lighthouse 13.6.0 was published on GitHub on October 27, 2026. Its release notes say it should reach PageSpeed Insights within about a week and ship in the DevTools of Chrome 159.
Live in PageSpeed Insights: Pollard, who works on web performance at Chrome, posted on Bluesky on November 2 that the release is live in PageSpeed Insights and that Chrome 159 is currently in Canary, the browser's test channel.
What happens to scores: Pollard said the update makes simulated FCP (first content shown) and LCP (largest visible element) more accurate and usually produces better scores. He added that it is not specific to single-page apps (SPAs) and is more likely to affect JavaScript-heavy sites.
Under the hood: the release notes say the Lantern simulation now uses Chrome's own render-blocking status for each request; that when the LCP element is text painted at the same time as the first content, it is estimated from the same data as FCP; and that HTTP/2 and HTTP/3 connections are modeled more accurately.
An open issue: on October 23 the Lighthouse team opened issue #17437 to investigate why, on some large JavaScript or SPA sites, the simulation estimates a much higher LCP than real loads show. The example given: 4.2 seconds measured versus 20.8 simulated.
Other new checks: the audit for AI agent resource discovery (ARD) moves to spec version 0.91. It looks for `/.well-known/ard.json`, a `<link rel="ard">` tag or a Link header, and flags manifests still at the legacy `ai-catalog` location. The robots.txt audit now recognizes the License directive, and both the robots.txt and llms.txt audits fail if the server answers with HTTP 429.

What changes and what doesn't

Lab scores change: the PageSpeed Insights and Lighthouse performance score comes from a simulated load on one device with fixed network conditions. Version 13.6 simulates differently, so the same page can get a different score with nothing changed.
Field data doesn't: the part of PageSpeed Insights that summarizes real visitors over the previous 28 days does not depend on that simulation. Google's documentation notes that good lab data does not guarantee a good real-user experience.
Your site doesn't: if the score rises, no visitor got a faster page. The measuring stick moved.
Comparisons do: a September report and a November report were not measured the same way. A jump in your trend chart from this week on may come from the version alone.

How to tell if this affects you

Check the version on every report. The footer of a PageSpeed Insights or Lighthouse report shows the Lighthouse version. A 13.5 report and a 13.6 report are not directly comparable.
Mark the switch in your tracking. If you log speed in a spreadsheet, dashboard or monthly report, note the date your reports moved to 13.6 so a jump isn't credited to your own work.
Check field data before celebrating. In PageSpeed Insights, the real-user section (28 days) tells you whether visitors notice anything. If it didn't move, the site didn't get faster.
Expect bigger swings on JavaScript-heavy sites. That is where Pollard expects the most difference. If simulated LCP looks wildly higher than real-world LCP, you may be hitting the open issue: compare with field data or Chrome DevTools' Performance panel before rebuilding anything.
If you publish an AI agent manifest under `ai-catalog`, Lighthouse will now flag it as a legacy location. The current spec uses `ard.json`.
If your firewall or host returns 429 to automated tools, the robots.txt and llms.txt audits will fail. Check whether the same rule also blocks crawlers you want to let in.

Sources

Updates: if Chrome 159 reaches stable or the Lighthouse team resolves issue #17437, it will be added here with a link.