You run developer relations at a small API company. This week your head of security asks a simple question: if a researcher finds a hole in our platform, where do they look to find out who to call? You open your own site and check. You have an llms.txt, written in an afternoon last quarter. You do not have a security.txt.
You are not alone, and the APIs.io catalog has the numbers. On November 1 the team behind it requested 13 machine-readable documents from the website of every provider it tracks: 28,378 distinct hosts, of which 26,886 answered. Of those, 7,588 served an llms.txt and 2,485 served a security.txt. The file that describes a site to a language model is about three times as common as the file that says who to call about a vulnerability. Only 1,223 hosts serve both, so your site, with one and not the other, sits in the crowd.
The rest of the table falls off the way you might guess. The llms.txt reaches 28.2% of reachable hosts and security.txt 9.2%. After that come OAuth authorization server metadata at 7.3%, content signals in robots.txt at 6.2%, the RFC 9727 api-catalog at 3.0%, OpenID configuration at 2.5%, and the Universal Commerce Protocol document at 2.5%. An A2A agent card shows up on 1.5% and apis.json on 0.6%. Overall, 10,251 hosts, 38% of those reachable, serve at least one of the 13. Most stop there: 6,715 serve exactly one, and only 41 serve eight or more. The post's reading is simple. An llms.txt is a text file anyone can write in an afternoon, while most of the rest need something behind them.
One pairing runs the other way. Of the 798 hosts with an api-catalog, 741 also serve an llms.txt, 93% against 28% across all reachable hosts. Sites that publish one of these documents tend to publish others.
Before you trust any of this, you should know how the counts were made. About one in ten reachable hosts, 2,556 of them, answered 200 for a nonsense path the team invented as a control. If you only counted status codes, every one of those sites would appear to support all 13 standards. So a hit means the body has the right shape: an agent card needs a name and an interface field, an api-catalog needs a linkset, a security.txt needs a Contact: line, and an HTML page never counts.
Then comes the part you would be tempted to brag about if you were selling agentic commerce. Of the 683 hosts serving /.well-known/ucp, 419 point at Shopify and 207 mention Wix. Only 57, about 8%, are neither. Reading 683 as 683 companies choosing agentic commerce would be a mistake, because the platforms made most of those decisions for their customers. A run on October 30 found 477. Of the 210 new hosts since, 206 are attributed to Wix. Two odd cases, kratix.io and www.syntax-bio.com, returned documents declaring shopping cart and checkout capabilities, and neither reads as a shop. The kratix.io document points its shopping endpoints at wixapis.com. The team says it has not established why those documents appeared, and does not know whether checkout works on any of them.
The post also turns the lens on its own author. These counts are floors. The team asked each provider's main host with a declared bot user agent, so an OAuth document on auth.example.com or an agent card on api.example.com reads as a miss, and so does any site that blocks bots. The content signals row is an upper bound, since those lines can come from a CDN default. The catalog is not the web, and includes small sites that came to it because they publish agent-facing documents, so these shares are not adoption across the internet. The shape tests are not validation, and the Wix attribution is a text match. And the catalog counts itself: apis.io serves 10 of the 13.
So what do you take back to your head of security? A well-known file proves the file exists. It does not show the company meant to publish it, or that anyone could act on it. The honest answer to the question is that you wrote the easy file first, as most did, and the one that tells a researcher who to call is still missing. Writing a security.txt with a Contact: line is as cheap as the llms.txt was. You can put it on the list before anything else.
Read the original: https://apis.io/2026/11/02/three-times-as-many-provider-sites-serve-llms-txt-as-security-txt/