How Many Sources Compete for AI Citations in Your Category
A measured answer from 16,475 observed AI answer runs: each category's citation market holds 236 to 4,025 distinct domains, the top ten hold 7 to 24 percent, and it takes 49 to 304 domains to reach half. What that means for where you aim.
Every AI visibility product sells you a leaderboard. Semrush, Ahrefs, Similarweb, BrightEdge, Conductor, Profound, Peec, AthenaHQ and Writesonic all ship a ranked list of domains and a position for yours. The implied instruction is climb into the top ten.
We measured what that top ten is actually worth. Across the 2026-09-23 release of the Machine Relations Index — 23,280 cited domains, 16,475 observed answer runs, 129,264 source observations, six engines, 130 days — the ten most-cited domains in a category hold between 7.0 and 24.2 percent of that category's citations. Reaching half of a category's citations takes between 49 and 304 distinct domains.
Your category's answer market is not a leaderboard. It is a long tail with a shallow head, and the position worth buying is not the one the dashboards sell.
Key takeaways
- The market is big in every category we measure. Distinct cited domains per category run from 236 at the small end to 4,025 at the large end, with a median of 1,299.
- The head is shallow. The top ten domains hold 7.0 to 24.2 percent of a category's citations. The most-cited single domain in a category appears in 6.7 to 28.9 percent of its answer runs.
- Entry is cheaper than the dashboards imply. The tenth-ranked domain in a category is cited in 2.8 to 9.8 percent of that category's runs. That is the real price of a top-ten slot.
- Category-local authority is mostly an artifact of the tail. 86.6 percent of all cited domains appear in exactly one category — and 46.9 percent of all cited domains were observed exactly once in 130 days.
- Condition on evidence and it inverts. Among the 228 domains with 50 or more citation observations, the median spans 5 of the 20 categories carrying data, and 14.0 percent are confined to one.
- Both shapes are real. 32 domains cleared 50 observations inside a single category; 41 cleared 50 across ten or more categories.
- Three categories are still unscoreable. iGaming and Betting, Industrial, and Local Services carry citation data but have not yet cleared the evidence floor on a single question shape.
How big is a category's AI citation market?
The Index groups measured questions into subject categories and buyer question shapes. Of its 25 taxonomy nodes, 20 carry citation data in the current release. For each of those, here is how many distinct domains an engine cited at least once, what share the top ten held, how many domains it took to reach half the citations, and the citation rate of the first- and tenth-ranked domain.
| Category | Distinct domains cited | Top-10 share | Domains to reach half | Rank 1 rate | Rank 10 rate |
|---|---|---|---|---|---|
| Legacy News Topics | 4,025 | 8.3% | 304 | 9.9% | 4.1% |
| Enterprise Software | 2,219 | 8.7% | 247 | 9.8% | 4.2% |
| Cybersecurity | 2,161 | 12.2% | 175 | 13.8% | 5.1% |
| Fintech | 2,151 | 8.1% | 207 | 10.1% | 3.7% |
| Healthcare Services | 2,078 | 10.6% | 214 | 16.5% | 4.0% |
| HR & Talent | 1,844 | 9.8% | 164 | 10.5% | 5.6% |
| AI Visibility & GEO | 1,762 | 14.4% | 139 | 25.6% | 7.0% |
| Consumer Products | 1,544 | 13.7% | 157 | 22.7% | 4.8% |
| Consumer Health | 1,304 | 18.8% | 95 | 28.9% | 7.5% |
| AI Security & Privacy | 1,299 | 15.3% | 104 | 24.4% | 6.1% |
| Martech & Advertising | 1,244 | 12.8% | 104 | 15.1% | 8.0% |
| Education & Training | 1,076 | 14.2% | 123 | 21.9% | 5.4% |
| Deep Tech & Hardware | 1,041 | 15.1% | 109 | 19.4% | 5.8% |
| AI Infrastructure | 1,039 | 21.2% | 70 | 25.7% | 7.7% |
| Consumer Finance | 1,008 | 23.6% | 53 | 26.4% | 7.4% |
| Emergent Prosumer | 867 | 15.0% | 118 | 21.6% | 4.0% |
| iGaming & Betting | 717 | 12.3% | 97 | 14.2% | 5.3% |
| Industrial | 704 | 7.0% | 188 | 6.7% | 2.8% |
| Family Software | 643 | 24.2% | 49 | 20.4% | 9.8% |
| Local Services | 236 | 18.2% | 59 | 16.7% | 8.3% |
Read the third column first. In Consumer Finance, the most concentrated real category, 53 domains carry half the citations. In Enterprise Software it takes 247. A leaderboard that shows you ten rows is showing you a tenth of one percent of the market in Enterprise Software and about a fifth of the domains that matter in Consumer Finance. Those are different businesses, and the same dashboard renders them identically.
What does it actually cost to reach the top ten?
Less than the framing implies, and it buys less than the framing implies.
The tenth-ranked domain in Industrial was cited in 2.8 percent of that category's runs. In Family Software, the most concentrated small category, it was 9.8 percent. Across all twenty, the tenth slot sits under ten percent of runs everywhere.
Here is Cybersecurity's actual head, with each domain's share of the category's 1,322 observed runs:
| Rank | Domain | Runs cited | Category citation rate |
|---|---|---|---|
| 1 | sentinelone.com | 183 | 13.8% |
| 2 | reddit.com | 172 | 13.0% |
| 3 | paloaltonetworks.com | 168 | 12.7% |
| 4 | microsoft.com | 134 | 10.1% |
| 5 | crowdstrike.com | 98 | 7.4% |
| 6 | huntress.com | 94 | 7.1% |
| 7 | gartner.com | 88 | 6.7% |
| 8 | linkedin.com | 81 | 6.1% |
| 9 | cynet.com | 79 | 6.0% |
| 10 | exabeam.com | 67 | 5.1% |
Three of the ten are security vendors citing themselves into the answer through their own owned pages. Two are general platforms. One is an analyst firm. The category leader appears in roughly one run in seven. Displacing rank 10 in Cybersecurity means being cited in about 67 more observed runs than you are now — a real target with a number attached, which is the opposite of what a percentile score gives you.
Fintech and HR & Talent look similar. Fintech's head runs stripe.com at 10.1 percent, linkedin.com at 9.0, airwallex.com at 6.9, deloitte.com at 4.5, openbankingtracker.com at 4.3. HR & Talent runs peoplemanagingpeople.com at 10.5 percent, linkedin.com at 6.9, forbes.com at 6.9, rippling.com at 6.7, g2.com at 6.6. In both, an independent review property sits inside the head alongside the category's largest vendors.
Is AI citation authority category-specific?
This is where the data sets a trap, and we walked into it before we caught it.
The headline number says yes: 86.6 percent of the 23,280 cited domains appear in exactly one category. That reads as a clean finding — authority is local, win your niche, breadth is a myth.
It is an artifact of the tail. 46.9 percent of all cited domains were observed exactly once across 130 days. A domain cited once can only ever appear in one category. The 86.6 percent is mostly counting domains that brushed an answer a single time, and it says nothing about the sources engines rely on.
Condition on evidence and the relationship reverses:
| Minimum citation observations | Domains | Single-category share | Mean categories |
|---|---|---|---|
| 1 or more | 23,280 | 86.6% | 1.24 |
| 2 or more | 12,366 | 74.8% | 1.46 |
| 5 or more | 4,977 | 60.5% | 1.89 |
| 10 or more | 2,251 | 48.6% | 2.43 |
| 25 or more | 673 | 27.3% | 3.84 |
| 50 or more | 228 | 14.0% | 5.71 |
The 228 domains with 50 or more observations hold 25.0 percent of all 115,066 citation observations in the release. Their median spans 5 of the 20 categories with data. The Index grades domains A, B or C by how much evidence stands behind their rate; 14 domains currently hold grade A, and every one of them appears in more than one category.
Grade C, a much larger set at 441 domains, is 27.4 percent single-category. So the pattern is monotone: the more an engine leans on a source, the more categories that source turns up in.
Two readings survive this, and they are both true. Domain authority in the classic link-graph sense still buys you nothing with an answer engine — that case rests on a different measurement and we have published the inversion. And breadth of observed citation travels with depth of it. Those are not in conflict. The first is about what earns a citation. The second is about what having earned many of them looks like from the outside.
Can a single-category source still win?
Yes, and 32 of them did. These are the domains that cleared 50 citation observations while appearing in exactly one category:
| Domain | Category | Citation observations | Confidence grade |
|---|---|---|---|
| omnimd.com | Healthcare Services | 105 | B |
| huntress.com | Cybersecurity | 94 | C |
| allaboutcookies.org | Family Software | 91 | C |
| useboomerang.com | Family Software | 80 | C |
| cynet.com | Cybersecurity | 79 | C |
| galengrowth.com | Healthcare Services | 78 | C |
| aha.org | Healthcare Services | 69 | C |
| unleash.ai | HR & Talent | 69 | C |
| safetydetectives.com | Family Software | 66 | C |
| petmd.com | Consumer Products | 63 | C |
Against those, 41 domains cleared 50 observations across ten or more categories. The widest are the ones you would guess — reddit.com in 20 categories on 2,042 observations, youtube.com in 20 on 1,441, linkedin.com in 19 on 1,116, forbes.com in 18 on 675, medium.com in 17 on 808, nih.gov in 15 on 490.
The practical read: a deep single-category position is achievable and it tops out around 100 observations, while the broad positions run into the thousands. If your category is the whole business, the specialist path is the one with a realistic finish line. If you are trying to be a source engines reach for by default, breadth is what that looks like when it works.
Which categories are not measurable yet?
The Index publishes a citation rate for a category and question shape only after that segment clears an evidence floor of 10 observations across 7 distinct run dates. Below the line it is marked collecting rather than scored, which is a statement about our evidence and not about the market.
Three of the 20 categories with citation data — iGaming & Betting, Industrial, and Local Services — have citations but no question shape above the floor. Martech & Advertising has one of seven shapes scored. If someone sells you a category score in one of those four, ask what evidence stands behind it, because ours is still accumulating. Five further taxonomy nodes carry no citation data in this release at all: Logistics & Freight, Physical Consumer, Professional Services, Sales & GTM CRM, and VC & Private Equity.
What to do with this
1. Replace the percentile with a run count. Rank 10 in your category is a number of observed runs, not a grade. In Cybersecurity it is 67. Ask your vendor for the denominator behind any score they show you; a rate without an observation count is a shape, not a measurement. Sielinski's March 2026 uncertainty work is the reason this matters: rankings move between repeated samples, so a position that is not carrying its evidence count is not carrying anything.
2. Aim at the half-line, not the head. The domains that reach half your category's citations number between 49 and 304. That set is where the answer actually gets built. Being inside it is a reachable goal in a way that displacing the category leader usually is not.
3. Treat your owned pages as a source class. Three of Cybersecurity's top ten are vendors cited through their own domains. Engines pull from vendor-owned material when it answers the question directly — the mechanics of how each engine selects and grounds sources are documented by OpenAI, Perplexity, Anthropic, Google and Microsoft, and each behaves differently.
4. Do not spend on breadth you have not earned. Breadth is a consequence of volume in this data, not a substitute for it. Domains appearing in many categories got there by being cited a lot somewhere first.
5. Measure on the surface that owns the answer. Per-engine behaviour diverges enough that a single blended number hides the thing you need. We track per-engine citation churn and answer-level co-citation separately for that reason. Google's own documentation on AI features in Search and its AI Mode announcement describe surfaces with different source behaviour again.
Frequently asked questions
How many domains compete for AI citations in a typical category?
The median category in the 2026-09-23 Machine Relations Index release had 1,299 distinct domains cited at least once across 130 days of observation. The range across the 20 categories carrying data was 236 to 4,025.
What share of AI citations do the top ten domains hold?
Between 7.0 and 24.2 percent, depending on the category. Family Software was the most concentrated at 24.2 percent; Industrial the least at 7.0 percent.
Is a top-ten AI visibility ranking worth chasing?
It is worth translating. A top-ten slot means a citation rate between 2.8 and 9.8 percent of a category's observed runs. That is a concrete target you can price. The rank by itself carries no information about how far away it is.
Do AI engines cite the same sources across different categories?
For the sources they lean on, yes. Among domains with 50 or more citation observations the median spans 5 of 20 categories. Across the full index 86.6 percent appear in a single category, but 46.9 percent of all cited domains were observed only once, which is what drives that figure.
Why do some categories have no published citation rate?
The Index requires 10 observations across 7 distinct run dates before it publishes a rate for a category and question shape. iGaming & Betting, Industrial and Local Services are still accumulating evidence, so their segments are marked collecting rather than scored.
Sources and method
Every figure above is computed from the public Machine Relations Index release dated 2026-09-23: 23,280 cited domains, 16,475 observed answer runs, 129,264 source observations, six engines, observation window 2026-05-10 through 2026-09-23, evidence floor of 10 observations across 7 run dates. The public dataset reports citation rates, rankings and evidence counts; it excludes raw cited URLs and provider payloads, and its correction record is public.
Per-category denominators are the sum of observed runs across that category's question shapes, and they total exactly the release's own published run count of 16,475. Category counts are of domains with at least one citation observation in that category. "Domains to reach half" is the smallest number of domains whose citation observations sum to at least half the category total. Confidence grades A, B and C are the Index's own evidence tiers.
Before publishing the breadth finding we checked it against the pipeline step that produces it, because a result that looks clean in one direction is usually the instrument. The single-category share is driven by the once-observed tail, which is why the conditioned table is the one that carries the argument. Related structural background: the long tail shape this distribution takes, schema.org article markup as the machine-readable layer engines parse, NIST on measurement practice, market-size context from Statista, and ongoing coverage of engine behaviour at Search Engine Journal.