AI assistant referrers: hostnames, evidence and dates
16 hostnames, 10 with a test or a vendor source, the rest marked unverified. All rows verified 2026-10-19. Open data under CC BY 4.0, version 1.0.0.
Last checked · How we check
Referrer table
| Hostname | Referrer | utm_source | Evidence | GA4 | Plausible | Matomo | PostHog |
|---|---|---|---|---|---|---|---|
| chatgpt.comChatGPT · Web | Partly | chatgpt.com | Third-party test2025-05Ahrefs test (May 2025): links from free accounts sent a referrer, inline links on paid accounts used noreferrer; source links carried ?utm_source=chatgpt.com. First reports of the parameter on more links: 13 June 2025. The mobile app was reported to send no referrer. Behaviour changed in October 2026 (see incidents). Source | Named | Named | Named | Named |
| chat.openai.comChatGPT · Web (older hostname) | Unknown | not documented | UnverifiedListed in third-party filters; we have no test or vendor document for this hostname yet. ChatGPT used this hostname before chatgpt.com; the assistant itself is named by the tools, the hostname is not. | Named | Named | Named | Named |
| perplexity.aiPerplexity · Web | Sent | not documented | Third-party test2025-05Ahrefs test (May 2025): web version sent a referrer; the desktop app sent none; mobile was not tested. Source | Not named | Named | Named | Named |
| www.perplexity.aiPerplexity · Web (www variant) | Unknown | not documented | UnverifiedListed in third-party filters; we have no test or vendor document for this hostname yet. | Not named | Named | Named | Named |
| claude.aiClaude · Web | Sent | not documented | Third-party test2025-05Ahrefs test (May 2025): every tested link sent a referrer. GA4's release note names Claude; SEJ reports that GA4's later documentation does not. Source | One source | Named | Named | Named |
| gemini.google.comGemini · Web | Partly | not documented | Third-party test2025-05Ahrefs test (May 2025): usually sent a referrer; Deep Research ("researching websites") used noreferrer. Source | Named | Named | Named | Not stated |
| copilot.microsoft.comMicrosoft Copilot · Web | Partly | not documented | Third-party test2025-05Reported to switch between sending and not sending a referrer over the months; the Windows app sent none. Table form after the Ahrefs test (May 2025). Source | One source | Named | Named | Not stated |
| edgeservices.bing.comMicrosoft Copilot · Edge sidebar / Bing (reported) | Unknown | not documented | UnverifiedSeen in third-party regex lists (weak evidence); not tested by us. | One source | Named | Named | Not stated |
| grok.x.comGrok · Grok on X | Partly | not documented | Third-party test2025-05Reported: the standalone Grok app sends no referrer, Grok inside X does. Hostname after a third-party table (May 2025). Source | One source | Not stated | Not stated | Not stated |
| grok.comGrok · Web | Unknown | not documented | UnverifiedListed in third-party filters; we have no test or vendor document for this hostname yet. | One source | Not stated | Not stated | Not stated |
| chat.deepseek.comDeepSeek · Web | Partly | not documented | Third-party test2025-05Reported: no referrer except for links in web-search citations. The source table does not name the hostname, so the hostname itself is unverified. Source | One source | Not stated | Not stated | Not stated |
| www.meta.aiMeta AI · Web | Sent | not documented | Third-party test2025-05Ahrefs test (May 2025): referrer sent. Source | Not stated | Not stated | Named | Not stated |
| chat.mistral.aiLe Chat (Mistral) · Web | Sent | not documented | Third-party test2025-05Ahrefs test (May 2025): referrer sent. Source | Not stated | Not stated | Named | Not stated |
| you.comYou.com · Web | Unknown | not documented | UnverifiedListed in third-party filters; we have no test or vendor document for this hostname yet. | Not stated | Not stated | Not stated | Not stated |
| iask.aiiAsk · Web | Unknown | not documented | UnverifiedMatomo names iAsk as a known assistant; the hostname and its referrer behaviour are unverified. | Not stated | Not stated | Named | Not stated |
| google.comGoogle AI Overviews / AI Mode · Search | Sent | not documented | Third-party test2025-05Not distinguishable: AI Overviews and AI Mode clicks are counted as google / organic, the same as classic results. Google's documentation counts them under Web in Search Console. Excluded from generated filters. Source | Not stated | Not stated | Not stated | Not stated |
How to read the table
- Referrer says whether the assistant passes a referrer when a person clicks a link: Sent, Partly (on some surfaces only), Stripped or Unknown.
- Evidence is a third-party test, a vendor document, our own test or an observation in logs. Unverified rows come from third-party lists; nothing else backs them, and strict filters leave them out.
- GA4, Plausible, Matomo, PostHog show whether the tool's documentation names the assistant. For GA4 we compare two sources: Google's release note and Search Engine Journal's account of the later documentation. "One source" means only one of them names the assistant.
- Dates are ISO dates. Evidence date is when the underlying test or document was made; verified is when we last compared the row with it.
None of this is measured by us yet. Most behaviour rows rest on a test from May 2025. Behaviour changes: see the changelog and the October 2026 incident.
What is not on the list
Google AI Overviews and AI Mode are on the list only as an ambiguous row: their clicks arrive as google.com and are counted as organic. Crawlers such as GPTBot or ChatGPT-User are not referrers; they are bots that read your pages. And any assistant we have no source for is missing rather than guessed. Send corrections and additions to hello@answertraffic.com.