llms.txt vs llms-full.txt: which one actually gets read?

## The experiment

We deployed /llms.txt and /llms-full.txt on 240 customer subdomains and logged every AI-crawler fetch for 30 days. Total: ~480,000 crawler hits.

## Fetch ratio (per page)

| Crawler | /llms.txt | /llms-full.txt |
|---|---|---|
| GPTBot | 8.2 fetches/wk | 3.1 fetches/wk |
| ClaudeBot | 5.1 | 2.4 |
| PerplexityBot | 12.3 | 4.8 |
| Google-Extended | 4.0 | 1.2 |

## What we learned

- **llms.txt is the discovery file.** Crawlers fetch it 2–3x more often than llms-full.txt and use it as a routing index.
- **llms-full.txt is the citation file.** When we removed it temporarily on 40 subdomains, AI citations in Perplexity for those businesses dropped 22% within 14 days.
- **Perplexity is the heaviest consumer** of both — by a wide margin.

## Recommendation

Ship both. llms.txt should be short, scannable, and link out. llms-full.txt should contain your full citable knowledge — definitions, FAQs, services, NAP, structured facts — formatted as clean markdown.