PageSpeed Insights Moves to Lighthouse 13.6, and Scores Can Jump
Chrome's Barry Pollard says simulated FCP and LCP are more accurate now and usually score higher, so a jump in your report may not be your work.
PageSpeed Insights now runs Lighthouse 13.6.0. Your lab score can change without anything on your page changing.
The new version rebuilds part of the simulator that guesses how fast your page loads on a slow connection.
Chrome’s Barry Pollard announced the switch on Bluesky, Search Engine Journal reports. He says simulated FCP and LCP are more accurate now and usually score higher.
Did your score go up this week? It might not be your work.
What changed in the simulation
PageSpeed Insights doesn’t test your page on a slow phone. It loads it at full speed, then a simulator called Lantern estimates the slow version.
The Lighthouse 13.6.0 release notes, dated October 27, list a batch of Lantern fixes. SEJ picks out two that touch your score.
- Render-blocking: Lantern now reads Chrome’s own render-blocking label for each file and falls back to fetch priority only when that label is missing.
- Text LCP: when your biggest element is text painted with the first content, LCP is now estimated from the same requests and tasks as FCP.
That second fix matters. Developer Ivan Akulov showed a Framer page with only text above the fold, where the old simulator put LCP far later than FCP.
Same element. Two very different times.
Worse, preloading the page’s JavaScript modules made his simulated LCP slower, though it helped the real page.
So who sees the biggest change?
Pollard says it’s more likely to hit JavaScript-heavy sites, and that the change isn’t specific to single-page apps, even though a developer had first spotted big gains on one.
The AI agent audit changed too
Lighthouse 13.6 also moves its Agentic Resource Discovery (ARD) audit to the newer spec. The file is now ard.json, not ai-catalog.json.
It now looks in these places, in this order, before it tries the old names:
- An Agentmap line in your robots.txt.
- A
rel="ard"link tag or Link header. - The file at
/.well-known/ard.json.
In 13.5, your site could show Not Applicable if it only used the new name. That’s fixed.
Still on an old ai-catalog path? The report now warns you that ARD tools don’t have to look there.
When it reaches Chrome
The notes say 13.6 should ship in Chrome 159’s DevTools. Chrome’s schedule, as SEJ read it on November 2, puts 159 in stable on December 8.
Until then, DevTools and PageSpeed Insights can disagree on the same page.
Why it matters
If you send PageSpeed scores to a client or your boss, this is the week your chart jumps. Before you take the credit (or the blame), check the version.
Check three things in each of your reports:
- The Lighthouse version, printed next to the emulated device.
- Whether your before and after runs used the same version.
- The field data block, shown next to the lab score.
A 13.5 run against a 13.6 run isn’t a fair test. You’d be comparing two simulators.
Look at the field data
Then open the field data in the same report: 28 days of real Chrome visits from CrUX. That’s real visits, and it’s what I’d look at first when you audit Core Web Vitals.
The lab score helps you find problems. I’d never treat it as the number that ranks you.
My read: this is good news if a simulator bug was punishing your site, and awkward news if you sell “we took you from 60 to 90” this month.
Running WordPress with a heavy theme? Take the higher score, but real speed work still decides what your visitors feel.
That said, Lighthouse still has an open issue where simulated LCP runs far above measured LCP on big JavaScript and single-page sites. The simulator is still being fixed.
Anyway, check the version first.
Common Questions
Why did my PageSpeed Insights score go up without any changes to my website in November 2026?
PageSpeed Insights switched to Lighthouse 13.6.0, which changed how Lantern simulates First Contentful Paint and Largest Contentful Paint. Chrome’s Barry Pollard says the new estimates usually produce higher scores, especially on JavaScript-heavy sites.
How can I tell which Lighthouse version a PageSpeed Insights report used?
Each report prints the Lighthouse version next to the emulated device. Compare two reports only when both show the same version, such as 13.6.0, and check the CrUX field data as well.
When will Chrome DevTools get Lighthouse 13.6?
The Lighthouse team expects it in Chrome 159 DevTools. Chrome’s release schedule listed Chrome 159 for the stable channel on December 8, 2026.
